Dr. DoBB'S ToURNALof
COMPUTER
(Calisthenics Orthodontia
Running Light Without Overbyte
A Reference Journal for Users of Home Computers
volume Five
(ijS The People’s Computer Company Series
Dr. DoBB'S JoURNALof
COMPUTER
(Calisthenics Orthodontia
Running Light Without Overbyte
)ine (Computers
ve
ts The People’s (Computer Company Series
run HAYDEN BOOK COMPANY, INC.
I H 1 Rochelle Park, New Jersey
Acknowledgments
Many thanks to all authors and readers who have contributed articles, ideas and il¬
lumination to the pages of Dr. Dobb's Journal. Many of the items found in these pages
would have been inaccessible to the microcomputer hobbyist, or available only at great
expense, had their creators not felt that immersion in the critical caldron of the comput¬
ing community were more important than financial compensation.
Much gratitude also goes to the Friends of PCC. They are a large! and loose-knit band
united by such ephemeral and fleeting moments as potluck dinners, spontaneous music
in the parks, coffee house synergisms,and occasional moments of genius. These Friends
keep us sane, and make microcomputing human.
Cover: Linocut of griffin by Wendy Palmer. The mythological griffin, half lion and half
eagle, has long stood as an enemy of ignorance.
Book production: Wendy Palmer and Associates,
Palo Alto, California
Index by Julie Anton, Palo Alto, California
Full-page computer art by David Dameron.
ISBN 0-8104-5492-0
Copyright© 1982 by People's Computer Company. All rights reserved. No
part of this book may be reprinted, or reproduced, or utilized in any form or
by any electronic, mechanical, or other means, now known or hereafter invented,
including photocopying and recording, or in any information storage and
retrieval system, without permission in writing from the Publisher.
Printed in the United States of America
123456789 PRINTING
82 83 84 85 86 87 88 89 90
YEAR
Dr. Dobb’s Journal
of Computer Calisthenics 6 Orthodontia,
Volu me Five
Editors Preface
And where will it lead?
That was the question posed in Dr. Dobb’s Journal, Volume III. It was a time when
a body of microprocessor knowledge had been accumulated, but the number of persons
with access to and understanding of that knowledge was extremely small. Manufacturing
techniques were being perfected, but costs were still high. The bandwagon was rolling,
but no one was holding the reins.
At least, that's the way it appeared.
Dr. Dobb's Journal was born in a time of chaos. Some fantastic new machines had
been bred in basement test tubes. The problem was how to optimize their potential?
Then a handful of radical-thinking idealists produced Tiny BASIC and a publication in
which to communicate the good news. More good things have been cropping up since
then, and now the magazine serves as a broad forum for the micro community.
To answer the original question, the revolution in microcomputing will lead when¬
ever we direct it. In the beginning, when there was very little momentum to the personal
computing movement, a handful of movers and shakers could do most of the guiding.
They saw to it that the power of small computers would indeed rest in the hands of indi¬
viduals instead of with corporations or government.
The movement has, of course, gained gigantic proportions as more and more people
have begun to grasp its significance and to reap its benefits. With its present inertial
force, many more guiding hands are needed to keep it on track, to preserve the original
dream. Dr. Dobb's Journal has kept pace by opening its pages to new authors, more free
thinkers and guiding lights.
The proliferation of hardware and software has required that we grow to meet the
challenge presented by our own idealism. In order to keep alive the concept of personal
computing power, we must riot only keep stride with technology, we must shape the fu¬
ture. We must be in the forefront, developing systems tools and refining the programming
languages,techniques and very concepts which will influence what small computers will
be able to do, and for whom
Lest we become too grandiose, too filled with the importance of our mission, we
have Doc Dobb's humbling influence. Always ready with a bit of irony and keen wit,
Doc sees to it that the pages of his journal remain open as a forum and that they do not
become a soapbox dominated by any particular group or prejudice. His philosophical
outlook is often expressed in such homilies as "Let a thousand lilies bloom . .." and "If
it's grist for the mill, we'll grind it." That view is tempered by another of Doc's sayings,
"The quick brown fox keeps his tail out of the lazy dog's mouth."
That is Doc's way of reminding us not to be influenced by any special interests. Its
broad, objective approach has enabled Dr. Dobb's Journal to serve the world as the lead¬
ing publication in its field. But more than a publication, it is a style of thinking which
makes technology work for humans — and not the other way around.
Marlin Ouverson
Editor
Contents
VOLUME 5, NUMBER 41, 1980
2 The History of CP/M Gary A. Kildall
4 An Overview of CP/M Compatible Software Steve Newberry
11 Go: A Utility Command Under CP/M Anthony Skjellum
13 Linking CP/M to George Morrow’s Cassette Interface Wayne Miller
15 Implementing a Tiny Interpreter with a CP/M Flavored C Les Hancock
24 ALS-8 to CP/M File Converter Hollis Frampton
26 Converter Listing
29 CP/M and CDOS Program Compatibility Jim Warner
32 Changing SPI Formatted Programs to CP/M Compatible Text MarkM. Zeiger
34 CP/M-Pen, Pen-CP/M Rod Hallen
37 Programming Pastimes and Pleasures Charles Wetherell
VOLUME 5 , NUMBER 42, 1980
46 TI 9900 Fully Reentrant Formatter Operating Under TIPMX Norman V. Walters
55 North Star Disk STOIC
56 Feature Enhancements for ADM-3A John Wakerly
59 A Table-Driven Assembler on CP/M Darrel J. Van Buer
67 A User Interface to APPLE-II Program Renumbering DeWitt S. Brown
73 Converting Binary to Decimal Dennis Allison
75 UCSD PASCAL Terminal Parameters Ronald G. Parsons
77 Programming Pastimes and Pleasures Charles Wetherell
79 A Microprocessor-Assisted Graphics System Griffith Hamlin, Jr. and Thomas Crockett
VOLUME 5, NUMBER 43, 1980
88 Mathematical Typography Donald E. Knuth
104 SYMBOL: Generating Symbol Table Alpha Listing on the H8 William W. Moss
108 TI9900: Fully Reentrant Formatter Operating Under TIPMX, Part 2
Norman V. Walters
121 Can You Afford to Retire? David E. Raeside
122 A Hex Keyboard with Applications for the 1802 ELF Martin Bronstein
VOLUME 5, NUMBER 44, 1 980
130 An Introduction to Algorithm Design Jon Louis Bentley
141 All the Secrets You Ever Wanted About Poly 88 BASIC Marvin A. Konopik
142 Meta II: A Syntax-Oriented Compiler Writing Language D.V. Schorre
151 A Northstar BASIC Cross-Reference Tool Titus Purdin
159 Some Useful Subroutines for a Z-80 Assembler John W. Carter
164 A Fast Fourier Transform for the 8080 Robert D. Fusfeld
169 Algorithm: A Monthly Algorithm Column Dennis Alliscn
VOLUME 5, NUMBER 4 5, 1 980
176 A Small C Compiler for the 8080’s Ron Cain
191 The C Programming Language D. M. Ritchie, S. C. Johnson, M. E. Lesk,
B. W. Kernighan
201 Structured Programming, C and tiny c Tom Gibson and Scott Guthery
205 Help with OSI’s CP/ M Lee Barker
207 Algorithm: A Monthly Algorithm Column Dennis Allisc n
209 MITS DOS - Disk to Disk Copy Routine Andrew Bender
216 An 8080 to Z80 Translator System Robert W. Dea
VOLUME 5, NUMBER 46, 1 980
226 A Survey of Computer Networks Art Kleiner
230 The Personal Computer Network (PCNET) Project Dave Caulkins
234 MCALL-C: A Communications Protocol for Personal Computers Tim J. Pugh, Jr.
239 Electric Phone Book
240 On Modems William Smith
242 Adding Arrays to FORTH Ralph Deane
243 ROM Byte-Finder for the Apple II Stephen E. Bach
244 The Errata of Computer Programming Donald E. Knuth
257 Random Ruminations of Networks of the Future Jonathan Sachs
259 Displaying 2 Columns with North Star O. K. Hudson
260 A Versatile Memory Dump in BASIC Hal Knippenberg
261 Conversion: ALS-8toCP/M Edward Elizondo
264 Algorithm: A Monthly Algorithm Column Dennis Allison
VOLUME 5, NUMBER 4 7, 1 980
272 ZX65: Simulating a Micro Richard M. Kruse
279 Harlie: A “No Programming” Computer J. L. Lawrence and Jay Sprenkle
282 Clean Starts for COSMAC 1861 Video Output Gary H. Price
284 PCNET Notebook Dave Caulkins
285 Programming Pastimes and Pleasures Charles Wetherell
287 Z-80 Circuit for the H-8 Ted T. Stowe
289 Indirect Addressing for the 8080 and Z-80 Anthony Skjellum
VOLUME 5, NUMBER 4 8, 1 980
312 A Runtime Library for the Small c Compiler Ron Cain
324 Thoughts on Small Systems and Monitors H. T. Gordon
330 Programming Pastimes and Pleasures Charles Wetherell
332 Polymorphic Tallis to the H-14 Printer Marvin Konopik
333 A Note on 6502 Indirect Addressing W. D. Maurer
339 Northstar X-Reference Tool John Holtrichter, Jr.
341 Hardcopy Device Driver Programs for CP/M Steve Willoughby
345 The Love Program Gary Gaugler
348 A Problem with Logic Probes David N. Bertollo
349 An Error-Correcting Record Linking Method Sylvan Rubin
350 Algorithm: A Monthly Algorithm Column Dennis Allison
VOLUME 5, NUMBER 49, 1 980
356 Even Further with Tiny BASIC Robert Hudson
364 Microcomputers as They Should Be Olav Naess
367 CP/M to UCSD PASCAL File Conversion Tor Sj0wall
371 Extended Source-Text Area and Label Capability for SC/MP N1BASM W. F. Long
373 Opcode Design: 9 or 16 Bits? H. T. Gordon
375 MFT: A Multiple File Transfer Utility Lawrence E. Hughes
382 A Cross Reference Program for Northstar BASIC Larry Hudson
392 Solution of Three First Order Differential Equations with an SR-52 Programmable
Calculator S. Andrew Yakush
VOLUME 5, NUMBER 50, 1980
400 N-Logs: A New Number Language for Scientific Computers Keneth A. Simons
406 Las Vegas Super Slot: A CP/M Game Machine Program Using Flashwriter I Graphics
David W. Friedman
418 Quick-Key: A North Star BASIC Statement Generator Leonard E. Garcia
423 TUTOR: A Foreign Language Vocabulary Trainer Gary D. Gaugler
425 Interfacing the WH14 Printer to Your Microcomputer’s Serial Port Is Simpler Than You
Think Lacliman Sippy
426 Program Documentation Freeman L. Moore
431 MOVIT William D. Loughman
432 6800 and 1802 Cross-Assembler for CP/M William C. Colley, III
434 A Proposal on Strings for FORTH Ralph Deane
439 A 6800 Video Display Program Kenneth Drexler
447 Index
About
People’s Computer Company
People’s Computer Company, the publisher of Dr. Dobb’s Journal, was founded in 1972 as
a non -profit source of education and information about computers. Bob Albrecht, one of the
founders, explained the inspiration for the company in the first issue of the PCC Newspaper ■.
“Computers are mostly used against people instead of for people, used to control people
instead of free them. It’s time to change all that. We need a People’s Computer Company.”
PCC has initiated a number of successful service-oriented projects in order to empower
people to take more active part in a society in which computers are a significant factor. It has
published a newspaper, three magazines, and several books on home/personal computing. It has
also operated a neighborhood computer center, a mail-order bookstore, a computer van, and has
sponsored telecommunications research (PCNET).
The main emphasis of the company has been small, personal computers - the kind anyone
can learn to use and many families can afford. ComputerTown, USA! is a major project begun
with financial assistance from the National Science Foundation. It provides a model of how to
make everyone in a small- to medium-size community “computer literate.” It shows how to use
local resources - public libraries and museums, schools, community centers, local businesses, and
donations of hardware and volunteer time - to give children and adults direct, hands-on ex¬
perience with computers. ComputerTown shares its experience and resources in a newsletter and
via various other services. Affiliates already exist in the United Kingdom, Europe, Australia, and
across the United States.
Dr. Dobb’s Journal was PCX’s second publication. The first issue was published in 1976 to
provide a short-term forum for the newly written Tiny BASIC language. Reader response was so
strong that it went into monthly production immediately. It has since led the way by focusing on
important advances, printing public domain software, and fostering vital reader interaction on
technical matters. Readers generally describe their experience with computers as intermediate to
extensive. About ten percent of them live outside the United States. Volumes One through Five
cover the first five years of DDJ’s publication, and are available in matching, bound volumes
from Hayden Book Company.
People’s Computer Compsiny grew from the same roots as the Whole Earth Catalog. They
were offshoots of the Portola Institute of Menlo Park, California, an organization investigating
and promoting the idea of alternative technology. For the founders of PCC, this meant learning
to use computers as a liberating force in society.
To make these ideals manifest, it has been necessary to think far ahead, to be creative and
innovative. PCC published the first personal computing periodical in 1972, a time when the
technical community at large found the thought of “personal” computers preposterous. Shortly
thereafter, the company produced the world’s first book of computer games. Now in its sixth
printing, What to Do After You Hit Return has been a model for many other publishers.
The PCC staff members have a wide variety of personal and professional interests and
experience. Their work stems from a conviction that the personal computing revolution is of
tremendous significance, and that familiarity with computers fosters confidence and greater
control over one’s life.
People’s Computer Company
Box E
Menlo Park, CA 94025
Dr. DoBB'S JoURNALof
COMPUTER
(Calisthenics ^ Orthodontia
Running Light Without Overbyte
Number 41 January 1980 Volume 5, Issue 1
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
All - CP/M Issue!
The Evolution of an Industry: One Person’s Viewpoint 6
Gary A Kildall
Overview of CP/M Compatible Software 8
Steve Newberry
Implementing a Tiny Interpreter with a CP/M-Flavored C 20
Les Hancock
CP/M-Pen, Pen-CP/M 39
Rod Hallen
GO: A Utility Command Under CP/M 16
Anthony Skjellum
CP/M and CDOS Program Compatibility 34
Jim Warner
... and, as always, even more
1
THE EVOLUTION OF AN INDUSTRY:
ONE PERSON’S VIEWPOINT
BY GARY A. KILDALL
Digital Research
P.O. Box 579
Pacific Grove, California 93950
1973....
I was sitting quietly at my desk when Masatoshi Shima
hurried into my office at Intel and asked me to follow him to
his laboratory down the hall. In the middle of his work bench,
among the typical snaggle of jumpers, oscilloscopes and multi¬
meters, sat a binocular microscope with spider-leg probes,
all of which were subjecting a minute piece of silicon to help¬
less investigation. I peered through the microscope at the en¬
larged regular patterns with particular interest. As a consult¬
ant, my job was to design and develop certain software tools
for Intel. One was Interp/80, a program which simulated
Intel’s newly evolved 8080 microprocessor to be used by Intel
customers on timesharing systems. As I searched for some¬
thing recognizable, I hoped my simulation resembled the
operation of Shima’s first 8080 chip which had finally come to
life.
My proposal to Intel had been simple: I would provide
them with a language, called PL/M, to replace serious systems
programming in assembly language. The compiler would
first be written in FORTRAN for operation on timesharing
computers and “cross compile” to the eight-bit processors.
Next, we would write a PL/M compiler in PL/M and “boot¬
strap” from the timesharing computer to a resident compiler
operating on Intel’s new Intellec-8 development system. The
first part was complete. PL/M cross compilers and Interp
simulators were implemented for the now-best-forgotten
8008, as well as the 8080. Programs had been written and
tested by Intel’s software group, consisting of myself and two
other people, and we were ready for the real machine. Things
were going well: the resident compiler would be the next
step.
Unfortunately, nearly all small computer systems in 1973
used paper tape as the backup storage device, with the ubiqui¬
tous model 33 Teletype serving as the nerve-shattering I/O
device. It was readily apparent that resident development
systems could r ot compete with timesharing services when
considering throughput, resources, and services. Still the
notion of a personal computer for software development in¬
terested everyone.
I became intrigued with a new device, called a floppy disk,
which, though designed by IBM to replace punched cards,
appeared to have much greater potential. The device was
ideal: over 3,000 times the data rate of a Teletype, each $7
diskette could randomly access the equivalent of 2000 feet
of paper tape. Best of all, the drive was priced at a low $500.
Due to a slight problem of undercapitalization, I found this
incredibly low price still a bit high. At that time, a smallish
company called Shugart Associates was in operation a few
miles up the road from Intel. Dave Scott, then marketing
manager at Shugart Associates, donated one of their 10,000-
hour test drives to the cause, complete with wom-out bearings
and a bearing repair kit. It was only later, as I sat in my
office at home, staring at the naked disk drive, that I realized
I had no cabinet, no cables, no power supplies, no controller,
and most distressing of all, no hardware design experience.
To make matters worse, no controllers were commercially
available, even if 1 could afford one.
After several abortive attempts at constructing an inter¬
face to my Intellec-8, it became readily apparent that my
efforts would be better directed toward the software aspects.
Page 6 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 41
2
Between projects I put together the first CP/M file system,
designed to support a resident PL/M compiler. The timeshar¬
ing version of PL/M, along with the Interp simulator, allowed
me to develop and checkout the various file operations to the
level of primitive disk I/O. A simulation is, after all, just a
simulation, and the inability to make that 10,000 hour drive
work for just one more hour was frustrating.
Shortly thereafter, in the fall of 1974, John Torode be¬
came interested in the project. I offered as much moral
support as possible while John worked through the aberra¬
tions of the IBM standard to complete one of my aborted
controllers. Our first controller was a beautiful rat’s nest of
wirewraps, boards and cables (well, at least it was beautiful
to us!) which, by good fortune, often perfoimed seeks, reads,
and writes just as requested. For agonizing minutes, we loaded
the CP/M machine code through the paper tape reader into the
Intellec-8 memory. To our amazement, the disk system went
through its initialization and printed the CP/M prompt at the
Teletype.
Anyone who has brought-up CP/M on a homebuilt com¬
puter has felt this moment of elation. A myriad of connections
are properly closed, bits are flying at lightning speeds over
busses and through circuits and program logic, to produce
a single prompt. In comparison to our paper tape devices,
we had the power of a S/370 at our fingertips. A few nervous
tests confirmed that all was working properly, so we retired
for the evening to take on the simpler task of emptying a
jug of not-so-good red wine while reconstructing battles,
and speculating on the future of our new software tool.
In the months that followed, CP/M evolved rather slowly.
Intel was experiencing enormous growth and all software
development was halted while new mangement structures
were instituted. Intel expressed no interest in CP/M, nor in
continuing any resident compiler work. Nearly two years
passed before Intel again took interest in resident software
tools, with their introduction of the ISIS operating system
and later, the resident PL/M-80 compiler.
Meanwhile, John Torode redesigned and refined our origi¬
nal controller and produced his first complete computer
system, marketed under his company name, Digital Systems
(which later became Digital Microsystems). The first com¬
mercial licensing of CP/M took place in 1975 with contracts
between Digital Sytems and Omron of America for use in
their intelligent terminal, and with Lawrence Livermore Lab¬
oratories where CP/M was used to monitor programs in the
Octopus network. Little attention was paid to CP/M for about
a year. In my spare time, I worked to improve overall facilities,
and added an editor, assembler, and debugger which were
predecessors of the current ED, ASM, and DDT programs.
By this time, CP/M had been adapted for four different con¬
trollers.
In 1976, Glenn Ewing approached me with a problem:
Imsai, Incorporated, for whom Glenn consulted, had shipped
a large number of disk subsystems with a promise that an
operating system would follow. I was somewhat reluctant to
adapt CP/M to yet another controller, and thus the notion of
a separated Basic I/O System (BIOS) evolved. In principle,
the hardware dependent portions of CP/M were concentrated
in the BIOS, thus allowing Glenn, or anyone else, to adapt
CP/M to the Imsai equipment. Imsai was subsequently li¬
censed to distribute CP/M version 1.3 which eventually
evolved into an operating system called IMDOS.
By coincidence, Jim Warren and I were both consulting
at Signetics Corporation during this time. Jim was then the
editor of DDJ, and pushed for sale of CP/M to the general
public. There was, at the time, a pervading paranoia among
software vendors who felt that any and all loose software
would be immediately “ripped-off ’ by this immoral group of
computer junkies. Jim’s faith in the industry, however, led
me to introduce the CP/M 1.3 system for sale on the open
market at $70 per copy. In the months that followed, the
nature of the computer hobbyist became apparent. In most
cases he was, like myself, in the computer industry and merely
wanted a personal computer for his own endeavors. CP/M
gradually gained popularity through a “grassroots” effect
and, to the amazement of the skeptics, the rip-off factor
was practically nil. A new company called Digital Research
was formed to support CP/M, develop new products, and
provide administrative functions.
It’s been nearly three years since CP/M’s initial introduc¬
tion, with several revisions and improvements. Although floppy
disks maintain their popularity, CP/M 2.0 is now offerred
to manage larger capacity hard disks which are becoming
more readily available. Customer needs and demands have
also led to the recent introduction of MP/M, a CP/M compat¬
ible multiterminal multiprogramming system for more so¬
phisticated applications.
More important, however, is that CP/M provides a manu¬
facturer independent basis for an evolving software market.
We all know that software is expensive to develop and support,
with numbers quoted in the hundreds of thousands of dollars
over the product lifetime. In a classical computer market¬
place, these costs are amortized over a few installations, re¬
sulting in seemingly outrageous prices. Active CP/M users,
however, number in the tens of thousands and can be reached
through any number of popular magazines. Thus, marketeers
reduce their prices substantially to interest a much larger
customer base. Software is sold profitably as an independent
commodity by a large number of responsible companies, and
the benefits to the consumer are clear. Competition forces
low prices and quality control, with selection among a wide
variety of software products. Currently, CP/M compatible
products range from word processing programs through bus¬
iness systems to a variety of language processors for BASIC,
FORTRAN, COBOL, PASCAL, and others. All are priced
in the $100 to $700 range. The future is, without doubt,
optimistic for producers and customers alike.
Number 41
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 7
3
An Overview
W*
I s
I * '•
Of CP/N
Compatible
Software
• -■
BY STEVE NEWBERRY
NEWBERRY MICROSYSTEMS
24225 Summerhill Ave
Los Altos, CA 94022 CP/M User’s Group Software
Most user’s group libraries represent a spectrum of program¬
ming interests and capabilities. The CPMUG library is no
exception. Most of the programs fall into one of four
categories:
1. Utility programs other than language facility programs;
2. Language facility programs, e.g., compilers, assemblers aid
interpreters;
3. Specialized device drivers which, e.g., interface a modem
board or a TVT controller or a printer to the system in
question; and,
4. Recreational programs, games.
The following programs are available from CP/M User’s
Group, 164 West 83rd Street, N.Y.C. 10024. The Price is
$8.00 per 8" floppy disk for domestic mailings and $12.00
foreign. CPMUG membership costs $4.00, and includes a
catalog of the library. As of this date (Nov 14, ’79) there
are 33 volumes iri the library. The diskettes will be referenced
in the sequel by the notation ‘x.y’ which means “Volume x,
program y”. Thus ‘XREF.ASM (8.27)’ refers to program
#27, of Volume #8, called XREF.ASM. The organization
of the volumes recognizes the difference between games and
non-games, so if you decide to purchase a volume (diskette)
for one or two of its programs, there is a good chance that the
rest of the volume will be of some interest as well.
Volumes 1, 6, 8, 14, 15, 16, 18, 19, 24, 25 and 29 are
primarily of the first and third categories: general utilities and
specialized device drivers. Working backwards through this list
(to get the most recently updated versions), we find:
Page 8 Dr. Dobb's Journal of Computer Calisthenics 8t Orthodontia, Box E, Menlo Park, CA 94025 Number 41
4
Steve Newberry is a graduate of Stanford University. A
member of ACM since 1966, member of the IEEE Computer
Society, he is an independent consultant, specializing in
contract programming and documentation.
Introduction
One of the reasons I use and recommend CP/M is that there
is a lot of very good software that runs under it. In what
follows I will give a necessarily sketchy overview of some
packages of which I have knowledge. I make no attempt to be
either complete or unbiased. There is only one computer game
that I care about, The Greatest Game Of All: PROGRAM¬
MING! Therefore, most of the packages that follow will be
found to reflect that outlook.
NON-COMMERCIAL SOFTWARE
By non-commercial I mean either public-domain or copy¬
righted but distributed very inexpensively.
UNLOAD.ASM (29.23) This is the CP/M version of the
ISIS OBJHEX utility which takes a COM file (binary load
module) and converts it to hex. This is a VERY useful tool,
Since CP/M lacks a linking loader. The CP/M utilities DDT and
save do, however, enable you to load (typically in low
memory) several COM (or HEX) files contiguously, to link
these manually (i.e., by patching in the link; addresses), and
then to SAVE the linked memory image to a COM file
origined at lOOh. Using UNLOAD, you can convert the COM
file to hex and then, again using DDT, relocate the HEX file
to any desired location. Warning: Only the source of
UNLOAD is given, and the Digital Research Macro assembler
is required for assembly (but you ought to have that anyhow).
This program alone is worth the $8.00, but there’s lots of
other good stuff on the volume.
COPY.ASM (1,3 and 25.17) A track-to-track diskette
copying routine (the second version is for Tarbell controller)
which is very fast and convenient to use.
FORMAT.ASM (25.18) Initializes a diskette, requires
Tarbell controller.
DUMP.COM (24.2) Updated version of (14.6). Allows
you to look at the contents of a diskette by file, by track, by
sector or by group (the sequence of sectors used by CP/M in
allocating disk space to a file), and allows you to directly alter
any byte on the disk. Used to recover inadvertently ERAsed
files or to recover (sometimes!) files w'tiich have been
otherwise lost. An invaluable tool! Three cheers for Sam
Sinser, the man who wrote it. Includes source code.
XDIR.COM (24.11) Another Sam Sinser goodie, this
prints out the directory of the indicated diskette, alphabetical¬
ly sorted, formatted so that it all falls on a single screen
display, and tells you how much space is left. Try it, you’ll
love it.
BYTEMOV.ASM (8.7) Driver program for either
Cromemco Bytesaver or Piiceon Program Saver from boards.
Ve ry elegantly programmed by Jeff Shook.
XREF.ASM (8.27) Use this to convert the assembly
listing from ASM or MAC (the Digital Research assemblers) to
a fully CROSS-INDEXED listing. An invaluable aid in docu¬
menting (and debugging) assembly code programs.
COMPARE.ASM (6.4) Compares two files, tells you
WHERE they differ (if they differ) and how long they are (if
they don’t). This is the sort of program, that you don’t use
often but that you’ll sell your soul to have when you DO need
it! (Like when PIP tells you that a filecopy has aborted on a
VERIFY error but won’t tell you WHERE—it KNOWS, but it
won’t tell—at such times COMPARE is a godsend.)
IDIR.COM (1.18)
ICOPY.ASM (1.17) Given an ISIS diskette, you can (a)
find out what is on it, and (b) copy what is on it to CPM
diskette. NICE!
Dr. Dobb's Journal of Calisthenics &
The above programs represent only a small fraction of the
utilities in the CPMUG library, but they are some of the ones
that I have on my system disk and use all the time.
Volumes 2, 4, 5, 7, 10, 11, 12, 16, 23, 30 and 31 are
primarily devoted to the second category,i.e., language facility
programs.
LLLBASIC.ASM (2.1 and 10.1)
LLLBASIC.COM (2.2 and 10.2)
LLLFP.ASM (2.4 and 10.3) Lawrence Livermore Lab
BASIC is in the public domain. The later versions are to be
preferred.
TEMYBAS.COM (2.8 and 11.7) Lichen Wang’s (public
domain) Palo Alto Tiny BASIC, patched for CP/M SAVE and
LOAD, with full documentation (2.9 and 11.8). The later
version is to be preferred.
BASIC.COM (30.5)
RUN.COM (30.7)
FPCONV.SRC (29.24)
FPDATA.SRC (29.25)
FPDMT.SRC (29.26)
FPPKG.SRC (29.27)
TRAN.SRC (29.28) Gordon Eubanks’ BASIC-E is the
best BASIC in the public domain. It is a semi-compiled BASIC
and is a precursor of the very successful CBASIC by the same
author (Volume 30 also contains the PL/M source if you care
to see how he did it). BASIC-E includes the transcendental
functions, string manipulation and CP/M file I/O. Floating
point arithmetic numbers are represented to slightly better
than seven digits of significance. Variable length strings and n-
dimensional arrays are both dynamically allocated. Line
numbers are required only when targeted by GOTO or
GOSUB. Identifiers may be any length and the first 31 charac¬
ters are significant. Execution is rather slow: the canonical
“FOR 1=0 TO 10000: A=5: NEXT I: END” takes about two
minutes and ten seconds to execute. A manual used to be
available from Digital Research.
BASIC/5.ASM (11.1)
BASIC/5.COM (11.2)
BASIC/5.DOC (11.3) This is Processor Technology’s 5k
BASIC adapted for disk. An alternative to LLL BASIC,
approximately the same size, but different flavor. Not in the
public domain.
PILOT Volumes 7 and 12 are devoted to John Stark¬
weather’s masterpiece; the former is for Intel MDS, the latter
for CP/M. If you are interested in writing Computer Aided
Instruction programs, then this is the language of choice —
it was designed for precisely that purpose. It can be EASILY
learned by children in kindergarten or by people who “hate
Orthodontia, Box E, Menlo Park, CA 94025 Page 9
5
Number 41
computers.” PILOT is in the public domain. Persons wishing
to obtain further information on PILOT would probably get
pointed in the right direction by Gregory Yob.P.O. Box 354,
Palo Alto, CA 94301, Telephone (415) 326-4039.
Z80ASM The Z80ASM package (16.15 through 16.21)
includes a running Zilog-mnemonics 8080/Z80 cross-assem¬
bler, source code for same, and some documentation.
MACASM.COM (16.8) This is a short macro assembler
(no source) with a small bug which could be rapidly located by
the DDT II debugger (see below in the commercial section).
ASMX.COM (16.1) This is another 8080/Z80 cross-
assembler (no source), recognizes extended-Intel mnemonics,
and is extensively documented in file VOLUME16.DOC and
(17.11).
STOIC Volume 23 is devoted to STOIC, a dialect of
FORTH which is well-suited to interactive real-time control
systems. The system includes a file handling system, an editor,
an interrupt handler, a rich assortment of floating and fixed-
point arithmetic routines and “much, much more.” WARN¬
ING: Learning to program in STOIC (or FORTH) is a non¬
trivial undertaking. Although its proponents regard it as a high-
level language, it is in fact a structured macro-assembly
language for a virtual stack machine. The experienced systems
hacker will take it in stride, particularly if he has a background
in assembly programming a zero-address machine, but the
neophyte may find it hard going at first.
PROCSELF.ASM (18.7) The source code for the classic
“Processor Technology Software #1”. A small, fast, dumb
assembler for non-disk systems, primarily of historical interest
as the first public-domain software for 8080 available to the
general public. Back in 1975, it and Microsoft BASIC were
almost the only systems software available for the 8080. Rest
in peace, old friend.
RATFOR.COM (26.4) This is a preprocessor which
translates a nicely structured language (called RATFOR) into
ANSI Fortran. It is extensively documented in the classic text
“Software Tools”, by Kernighan and Plauger. Some slight
amount of editing is required to reconcile the emitted
FORTRAN declarations to the conventions recognized by the
Microsoft FORTRAN compiler. Although I no longer
remember the specifics, a couple of macros in ED does the job.
I’ve done it myself—it’s no big deal.
ALGOLM.COM (28.10)
good news: ALGOLM, ALGOL-60 and PASCAL are
fundamentally just variant dialects of the same language, and
therefore conversion of programs from one dialect to the other
is, in the general case, largely a matter of reconciling the
declaration-formats. Since there is a prodigious amount of
PUBLISHED software in ALGOL-60 and in PASCAL, it
follows that ALGOLM is not merely elegant (which certainly
it is), but REALLY useful as well! Here are some of the
characteristics of ALGOLM:
Three types of variables, signed integer, signed decimal and
string. Decimals may be declared with up to 18 digits of
precision and strings may contain up to 255 characters.
Decimal precision and string length may be represented as
integer variables which are assigned actual values at run time.
Arrays may be of type integer, decimal or string, may have
up to 255 dimensions, and dimension bounds may be
represented as integer variables which are assigned actual
values at run time.
Control structures are: BEGIN, END, FOR, IF THEN, IF
THEN ELSE, WHILE, CASE and GOTO.
BEGIN/END blocks may be nested to nine levels. Variables
declared within a given BEGIN/END block are only accessible
from within that block, and run-time storage space for such
variables is de-allocated upon exit from that block.
Functions and procedures may take parameters (call-by-
value only) and may be called recursively.
ALGOLM is semi-compiled and therefore both compact
and reasonably fast in execution. (The canonical benchmark
ran in one minute and five seconds.)
The ALGOLM package is well documented and there are a
number of sample programs.
TBASIC The complete package consists of Volumes 31
and 32. TBASIC is said to be “upward compatible” to Micro¬
soft 8k (Release 4.0), and is very well documented. The editor
is a vast improvement (to my taste) over that in Microsoft
BASIC, and is rather similar in style to ED. TBASIC has
several features not found in other BASICs. ASSIGN and
DROP commands permit assignment/de-assignment of up to
10 physical devices to any of 6 logical I/O devices. Long
variable names and non-numeric labels are permitted.
Arguments may be passed to subroutines, and local variables
may be declared. Linkage to machine-language subroutines is
convenient (CALL command). The bad news is that I was
unable to get the CSAVE (to disk) to work. But I imagine that
the version which is sold by Tarbell (for $36.00) has that
fixed. TBASIC IS FAST: THE CANONICAL BENCHMARK
(SEE BASIC-E ABOVE) RAN IN TEN SECONDS FLAT! All
in all, a very well thought out alternative to BASIC-E.
RUNALG.COM (28.11) Volume 28 is one of the most The balance of the CPMUG library is largely devoted to
outstanding software values that I know of. It contains, in games (except for volume 9, which is a General Ledger
addition to the ALGOL package, a set of database, inventory package for Microsoft 12k Disk Basic Version 4.0, and for
and mail-list programs. But it is the ALGOL package which is volume 33, which is a very serious set of programs for auto-
so utterly mind-blowing. Like BASIC-E, it is the product of mating aircraft search-and-rescue operations),
the Naval Postgraduate School in Monterey, and is an
intelligent and thoroughly reasoned adaptation of a classic WARNING!!! WARNING!!! WARNING!!!
general-purpose programming language (in this case, ALGOL-
60) to the CP/M environment. The majority of the CPMUG programs have never heard of
First, the bad news: No linkage to assembly-language sub- lower-case ASCII. Fortunately, the assembly-source code is
routines and no built-in transcendental functions. But now the generally given, so this problem is easily fixed: Invoke ED with
Page 10 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 41
6
the source file. Look for an instance of ‘MVI C,l’ (or
‘MVI C,l’ if tabs are used). You are looking for the set¬
up for a system call “read console” (Function #1, see p.7,
CP/M Interface Guide). The command ‘brnfMVI C.IZOtt’
(or ‘brnfMVI C,l’) will quickly tell you how many such
lines there are, (if any). If this draws a ‘BREAK AT
AZ\ then there will be an EQU statement setting something
like ‘CONSINP’ to 1, so look for that. Then follow the ‘CALL
BEiOS’ or ‘CALL 5’ (just after the ‘MVI C,l’) with code to
mask out bit 5 of all characters between 61 h and 7ah. Now
assemble and enjoy.
Two other sources of CP/M compatible public-domain
software are:
The Tarbell Public Domain Software volume, available from
Tarbell Electronics, 950 Dovlen Place, Carson, CA 90746 for
$10.00 (domestic). This is a collection of all of the Tarbell-
dependent software in the CPMUG library (nought together
on a single disk.
The fig-FORTH package. The diskette is $35.00, available
from FORTHRIGHT ENTERPRISES, P.O. Box 50911,
Palo Alto, CA 94303. The documentation consists of two
volumes, the Installation Manual and Glossary, and the
Source Code listing + aids. These are available from the
FORTH INTEREST GROUP, P.O. Box 1105, San Carlos,
CA 94070 at $10.00 per volume.
fig-FORTH is a standardized FORTH which ports
smoothly between 8080, 6502, PDP/11 and very possibly
several other machines as well. Its proponents regard it as the
greatest thing since the invention of toilet paper, and they
may well be right. (But see the comment on STOIC above).
COMMERCIAL SOFTWARE
The following are packages which either I own and use on
my own system, or which I do not own but have used on some
other system, or which I know of only indirectly through the
testimony of colleagues and/or study of the documentation.
Here again the selection is far from complete and reflects my
own personal biases and interests. For a broader overview of
the commercially available packages which run under CP/M,
consult the advertisements of LIFEBOAT ASSOCIATES,
2248 Broadway, NY, NY 10024.
Editors and Output Formatters
WORD-STAR WORD-MASTER is ED with a cleaner
protocol for inputting and outputting subfiles, a more power¬
ful macro facility (conditional termination and nesting) and,
in addition, a VIDEO MODE in which the alterations to text
are dynamically monitored on the display screen as the edit
commands are entered. WORD-STAR is the screen editor
module of WORD-MASTER, plus an output formatter which
is ;ilso dynamically monitored on the display screen. This is
REALLY powerful, since you can see how the page sets up
as you enter the formatting commands. It also has some other
goodies, e.g., a menu-driven installation progiam which tailors
the editor/formatter to a number of video terminals and hard
copy printers, including the DIABLO and QUME daisywheel
printers.
If you already have extensive experience with ED (or any
of the other sons-of-TECO), and/or if you already have a
Dr. Dobb's Journal of Calisthenics &
formatter that you like (or NEED a formatter that auto¬
matically generates a sorted index), then WORD-STAR is less
attractive than WORD-MASTER. But if your text-entry is to
be done by inexperienced personnel, then WORD-STAR
would more than justify its purchase price by increasing the
output of a newly trained operator. Both packages are
SUPERBLY documented-an outstanding job. WORD-
MASTER sells for $125.00, and WORD-STAR for $495.00.
TEX This is the text formatter offered by Digital
Research. It offers the standard controls, pagination, margins,
line length, paragraphing, etc., and is entirely adequate for
letters or short brochures. There is no user-defined macro
facility. Documentation is very good, with many examples.
TEX sells for $85.00.
TEXTWRITER III This has all the functions of TEX, plus
several extremely powerful capabilities for the generation of
form-letters and sorted indexes. The form-letter feature will
either take the names and addresses from a diskfile, or stop
and prompt the operator to enter them manually. The
indexing feature allows you to flag key-words (as they occur
in the text) for inclusion in an index. Upon command,
TEXTWRITER III will compile a sorted index with appropri¬
ate indentations. For tech writers this is an invaluable aid. The
documentation is quite good. The power of the package, if
you leave out the form-letter and sorted-index feature, is
about the same as other formatters. There is no user-defined
macro facility. TEXTWRITER III sells for $125.00 and is
available from LIFEBOAT ASSOCIATES.
TSC TEXT PROCESSING SYSTEM If you don’t need
the sorted-index feature you should look into the TSC TEXT
PROCESSING SYSTEM, available from Technical Systems
Consultants, Inc., P.O. Box 2574, West Lafayette, Indiana
47906. This sells for $50.00, is patterned after the UNIX
utility NROFF, and is sold with a manual which INCLUDES
THE ASSEMBLY SOURCE CODE! This is an EXTREMELY
powerful package, with 27 memory-registers, user-defined
macros, conditional macro-execution and access to diskfiles.
There is a pre-defined set of macros which includes form-
letter generation. I’ve used it since it first came out and have
never had a complaint.
ASSEMBLERS
MAC In addition to the ASM assembler which comes as
an integral part of the CP/M package, Digital Research also
markets a macro assembler, MAC, which does not yet support
relocation, but otherwise is very similar to the Intel macro
assembler, ASM-80. MAC allows long (up to 16 characters)
identifiers and puts out a special symbol table which is used by
the SID debugging package (see below). The MAC package
includes a set of macros called SEQIO.LIB (which VERY
much simplifies interfacing assembly-level programs with the
operating system), and another set of macros called Z80.LIB
which enable MAC to assemble Z80 op codes. The Z80 facility
utilizes extended-Intel mnemonics, rather in the style of the
TDL/Xitan assembler. The documentation consists of a well-
written tutorial and includes lots of worked examples. It got
me started sooner than would have been the case had I ONLY
the Intel “8080/8085 ASSEMBLY LANGUAGE PROGRAM-
Orthodontia, Box E, Menlo Park, CA 94025 Page 11
7
Number 41
MING MANUAL (Order Number 9800301C)” to work with.
However, I did find it necessary to purchase the Intel manual
in order to fill in certain gaps in the tutorial treatment. (The
Intel manual was only $5.00, so no big deal.)
MAC will assemble any source code accepted by the Intel
ASM-80 assembler documented in the above manual, EXCEPT
the relocation pseudos, ASEG, CSEG and DSEG. The MAC
package sells for $100.00 and I recommend it highly.
MACRO-80 The Microsoft MACRO-80 package is
available either separately at $150.00, or as a part of either of
the Microsoft BASIC or FORTRAN compiler. It is said to
conform to the Intel ASM-80 specification in all respects, and
the package includes a Linking Loader and Library Manager.
The documentation is adequate. (But see remarks on
FORTRAN compiler below).
SMAL/80 SMAL/80 is for those who need to write
assembly level code on an occasional basis, but are not yet
familiar with the 8080 instruction set mnemonics. It is a
Structured Macro Assembly Language which uses a semi-high
level notation convention which shows a family resemblance
to the C language. (The original version of SMAL was
developed by C. Popper at Bell Labs.) Control structures are
several flavors of brackets (BEGIN/END, DO/END, [/],
{/ }), IF < condition > THEN < statement >, IF < condition
THEN < statement > ELSE < statement > and loop controls
LOOP < statement > REPEAT and LOOP < statement
REPEAT WHILE < conditions THE MACRO PROCESSOR
PERMITS NESTING TO ANY DEPTH AND RECURSION.
Although it can. be cogently argued that SMAL should be
used even by experienced 8080 assembly programmers, (be¬
cause of the enhanced readability of the code), I doubt that
many will be convinced: The sensation is one of “too many
extra keystrokes for too little payoff.” The documentation is
in the Bell Labs style, clear, succinct and complete. SMAL/80
sells for $75.00.
SP80
SAL/80 These two packages represent a middle way
between SMAL/80 and straight macro-assembly programming.
They are libraries of macros which provide control structure
macros for specific macro assemblers. SP80 has versions for
the TDL/Xitan macro assembler, the Digital Research MAC,
“the Intel macro standard and MACRO-11 (PDP-11). I have
not seen this package or its documentation, only the
promotional literature, but I am myself the author of SAL/80,
and it would appear that the two packages are quite similar.
The SP80 package sells for $95.00 from SP80, P.O. Box 2745,
Reston, VA 22091.
SAL/80, in addition to the library of control structures,
contains a library of utility macros, such as, e.g., multiplica¬
tion, division, string move and search, output string to console,
etc., and will go into distribution in February for $50.00,
available from Newberry Microsystems, 24225 Summerhill
Ave., Los Altos, CA 94022.
BASIC
MICROSOFT BASIC (MBASIC) The “Industry
Standard” is, of course, MBASIC by Microsoft. It is fast (as
semi-compiled languages go) executing the canonical bench¬
mark in 28 seconds. Unlike most semi-compiled systems,
MBASIC does the translation to intermediate code during
program entry, so the translation process is invisible. The inter¬
mediate code is extremely compact and program development
time is greatly reduced by the continuously interactive nature
of the process. You enter some code, test it, modify it until
satisfied, and then SAVE it to disk. The current release has
overcome the shortcomings of most other BASICs: you can
now use long variable names, loops may be written in
structured fashion with the WHILE/WEND statement form,
and conditionals may be nested. MBASIC has evolved into
quite a civilized programming language. Moreover, MBASIC
can be compiled to native code on the Microsoft BASIC
compiler. Thus, the convenience of interactive program
development can be combined with the speed of native code
compilation—a truly impressive (and USEFUL!) achievement.
MBASIC goes by the name of ‘Disk Extended BASIC’ and sells
for $300.00. The MBASIC compiler sells for $350.00.
CBASIC II CBASIC grew out of BASIC -E by the addition
of bed arithmetic to fourteen places of significance, the
WHILE/WEND control statement, integer variables, chaining
with common variables, PRINT USING and improved file¬
handling capabikties. A number of very useful data-processing
packages (e.g., accounting, database, merge-sort etc.) have
been written in CBASIC and field-tested for several years.
CBASIC sells for $109.00.
COMPILERS
FORTRAN FORTRAN-80 by Microsoft is being
distributed by a number of firms under a number of names.
There are a zillion copies out there and running. It’s been in
distribution for several years now and is (presumably) well
wrung out. It conforms to the ANSI ’66 standard (except for
COMPLEX) and includes the MACRO-80 assembler, Linking
Loader, Library Manager and a library of standard subroutines.
The documentalion appears to be complete but reads more
nearly like a design spec than a user document.
PASCAL/M Written by DIGICON and distributed by
Digital Marketing, 2670 Cherry Lane, Walnut Creek, CA
94596, (415) 938-2880, Pascal/M is a recent arrival on the
CP/M scene, and one most welcome. It is source-code
compatible with UCSD Pascal, and hence is an almost “full
spec” Pascal. The following restrictions apply: No parameters
of type Procedure or Function. A File is NOT allowed as a
component of a structure. The procedure DISPOSE performs
no function. (However, MARK and RELEASE are provided to
manage the heap.) Standard procedures PACK and UNPACK
are not provided. A GOTO is not permitted to jump out of the
procedure/function in which it occurs. (However the EXIT
procedure of the UCSD version Is provided). Digicon lias
designed a new 'drtual machine (new P-codes) and two inter¬
preters are available, one for 8080 and one for Z80. (I have the
Z80 version arid it is FAST. The canonical benchmark
executes in 10 seconds.)
The package consists of the compiler, the interpreter, a
runtime library iind a set of installation programs. I brought
my copy up in just the time that it took to insert the diskette
and execute the INSTALLP program. (There is another
program for tailoring the interface to particular consoles, but I
Page 12
8
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Msnlo Park, CA 94025
Number 41
did not have to use it.) The documentation is concise without
being excessively terse. It sells for $350.00 and I think it’s a
real winner.
PASCAL/Z This is a native code compiler for a subset of
Pascal. Missing are floating point, variant records, the ability to
pass procedures/functions as parameters and (SOB!)
POINTERS. This assessment is based on the documentation
which prevailed almost a year ago, before they (Ithaca
InterSystems) had a CP/M version. The documentation of the
compiler was rather scanty, suggesting that the product was, at
that time, VERY new indeed. It sells for $275.00 and merits
further investigation.
WHITESMITH’S C Compiler This is a BIG compiler. It
compiles the full spec C language as set forth in Kemighan and
Richie’s book “The C Programming Language” (Prentiss-Hall,
1978). The package includes the compiler, “narrative
assembler”, linking loader, library and a set of installation
programs. The documentation is in the style of the UNIX Pro¬
grammer’s Manual, encyclopedic but terse. 'Hie installation is
simple: plug in the diskette and follow instructions. The
compiler consists of four modules (including the “narrative
assembler”), which total out to 156 Kb. There are lots of error
diagnostics and substantial code optimization is performed.
The first module is the preprocessor which does macro ex¬
pansions. This is overlaid by the PI pass, v/hich does lexical
and syntactical analysis and some optimization. PI is then
overlaid by P2 which completes the optimization and emits
the intermediate code in “narrative assembler” notation. (This
is a highly condensed assembly level notation which, like that
of SMAL, is reminiscent of C.) The assembler, called ‘A-
natural’, overlays P2 and generates a relocatable load module.
The compilation process is initiated by calling a SUBMIT file
wliich handles the overlaying and creation and deletion of
scratch files. The whole operation is somewhat faster than a
PLM compilation, but not a whole bunch. The link-load
process is also handled by a SUBMIT file, and generates a COM
file.
Bill Plauser (at Whitesmith’s) tells me that there are about
150 copies in the field to date and that the feedback indicates
that the system is very stable. The Whitesmith’s C Compiler
sells for $630.00 from LIFEBOAT ASSOCIATES. If you want
an optimizing compiler for a structured language, this is the
one.
BDS C Compiler This is the work of Leor Zolman (at
M.I.T.) and realizes a subset of C. There is no data initializa¬
tion, no long types, no floating point, no STATIC or
REGISTER declarations, and not a whole bunch of optimiza¬
tion. However there is still plenty left for systems program¬
ming, and the package includes a linking loader and library
manager. Tom Gibson (of Tiny-c Associates) tells me that he
and his associates have been using the compiler with uniformly
satisfactory results. The compiler generates relocatable load
modules for 8080, the linking loader link/loads (multiple)
object file(s) into a COM file. The documentation (again
quoting Tom) is written in the style of, “Here’s how to use
my compiler”. The BDS C Compiler sells for $110 including
the Kemighan & Richie book cited above.
BASIC See MBASIC, above.
Dr. Dobb’s Journal of Calisthenics &
A GREAT WAY TO LEARN STRUCTURED
PROGRAMMING
TINY-C This is a tiny masterpiece. The documentation is
so good that it can (and should) be used as an elementary text¬
book. The tiny-c language facility consists of a machine-
dependent interpreter (currently available, 8080 and PDP-11),
and a Program Preparation System (PPS) written in tiny-c
(and hence machine independent). PPS comprises an editor
and run-time monitor. This results in an interactive program
development system which is as convenient to use as any of
the interpreted BASICs. You enter the program, test it, revise
it, retest, etc., and write out to disk without having to change
environment. When runtime errors are detected, the monitor
halts execution and gives remarkably good diagnostic mes¬
sages. UNlike the BASICs (with the exception of TBASIC) the
editor is both pleasant to use and a preparation for bigger and
better editors. Similarly, the language tiny-c.
Although tiny-c is, indeed, a VERY tiny C, it is nonetheless
quite adequate for getting taste of the “hows and whys” of
full-scale languages. Indeed, the expressive power of the
language is comparable to the systems language XPL (the
forerunner of PLM), and literally hundreds of compilers have
been written in XPL! Tiny-c has IF/ELSE, WHILE, RETURN
and BREAK for control-structures, integer and character for
data types, one-dimensional arrays for data-structures, and a
pointer convention which permits call-by-reference as well as
call-by-value. Not too shabby!
The source code of PPS, together with several worked
examples provide excellent models of style and program
structure. PPS allows you to load any number of program
modules, which are then “linked” by the runtime monitor.
Provision is made for linkage to machine-code subroutines.
The assembly source of the interpreter is given together with a
34 page analysis of its anatomy and functional behavior.
Finally, there is extensive systems-level documentation to
facilitate the installation of the system on non-CP/M systems.
The CP/M installation is essentially a matter of inserting the
disk and calling the interpreter and PPS. Instructions are pro¬
vided for tailoring PPS to systems with more than 24Kb. An
appendix contains Newsletter updates. Tiny-c sells for $75.00
and is distributed by tiny-c associates, P.O. Box 269, Holmdel,
N.J. 07733.
DEBUGGING AIDS
DDS-n This is the best debugging tool I have ever used. It
is comparable to the ICE software on the Intel MDS system.
DDS takes over the video display screen (you can toggle back
to the program-generated display at will) and maintains a run¬
ning display of:
the value of the stack pointer, the top five words on the stack,
the five words pointed at BY the words on the stack (dis¬
played in both hex and ASCII)
the next five instructions, disassembled (and the first byte
also displayed in hex), beginning with the current instruction
the AF, BC, DE, HL registers together with the value of the
PC at the instruction PRIOR to the current instruction,
including the ASCII interpretation of the A register and
Orthodontia, Box E, Menlo Park, CA 94025 Page 13
9
Number 41
mnemonic representation of the condition flags, and the hex
contents of the memory words pointed at by the BC, DE and
HL registers, and a DDT-like display (in either ‘D’ or ‘L ’
mode) of any chunk of memory you wish to look at.
There is also a display, the “call-stack”, which shows the
last five return-addresses stacked as the result of a call, and
you can choose to be notified whenever a subroutine returns
to an address other than that which was stacked when it was
called (think about that!).
You can choose to be notified of a LOT of behaviors: if the
program references data outside of a predefined range, or
when the PC goes out of a predefined range, or when the
program references a given location, or when the SP goes
beyond a predefined range, or when the program IS ABOUT
TO store at a predetermined location, or when a given register
or memory byte/word attains a given value. You can do any
and all of the fill, insert, display, move etc., commands usually
found in most debug monitors, including all the flavors of
breakpoints imaginable. You can single-step or two-step or
n-step, I mean you have that program by the short-hairs!
The documentation is excellent, even to the point of
including a nine-page explanation of what assembly program¬
ming is all about. (I think that qualifies as overkill.) The
package is available in off-the-rack versions for either VDM-1
or ADM3A video displays, and can be patched to run on any
display which has x-y cursor addressability. I have only two
criticisms of the package: the time and space given to a
tutorial on assembly-language programming would have been
more usefully employed in outlining the patching procedures
for non-VDM/ADM displays, and I wish to God that the disas¬
sembler that drives this program understood about Z80 code.
Distributed by PRS, 257 Central Park West, New York City,
N.Y. 10024, and selling for $65.00, DDS-II is one of the great
bargains of all time. No joke.
SID Digital Research’s update of DDT, the Symbolic
Instruction Debugger adds three instructions to the DDT
vocabulary, two utilities (TRACE and HIST) and allows you
to specify addresses by the labels assigned them in the source
code as an alternative to the hex representation. While certain¬
ly it is very nice to be relieved of the need to refer back and
forth to the listing to figure out the logical signficance of hex
addresses, I haven’t really got much good out of that feature,
since when I’m doing that kind of debugging I’m talking to
DDS II instead. But the extensions to the command set,
particularly the hex arithmetic and the pass counter command
constitute a signficant enhancement of DDT.
The TRACE utility will compile a backtrace record of the
program addresses executed PRIOR TO hitting a specified
breakpoint. This is one of those “you don’t need it often, but
WHEN you need it, nothing else will do” utilities. Similarly,
the HIST utility profiles the activity regions of a program in
execution, enabling you to identify the “hot spots”. Empiri¬
cal studies have shown that most programs tend to “spend
90-95 percent of their time executing 5-10 percent of the
code.” Thus an improvement of even rather modest propor¬
tions in a critical area will have more impact on over-all
execution speed than a dramatic speedup of the relatively
idle areas. The HIST utility justifies the price of the package.
SID sells for $85.00 and an updated version which knows
about Z80 code is in the works.
Page 14
10
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
A Utiility Command
■ Under CP/M ■
BY ANTHONY SKJELLUM
1S95 Shenandoah Road
San Marino, CA 91108
No facility is provided under CP/M to reexecute a machine
language program already residing in the transient program
area, nor is there a direct facility for loading binary files
(.COM files) into the TPA without executing them except
with the use of DDT, the debugging tool. However, both
these functions can be performed through the CCP (central
command processor) by way of two programming “tricks.”
A special command must be created under CP/M in order
to reexecute a program. This is done by way of a “null”
.COM file. Using the CCP “SAVE” command, such a file
may be created as follows:
SAVE 0 @.COM
When “<® <CR>” is typed at the console. CP/M will search
the directory for “@.COM” but will not load any new bytes
into the TPA since the program has zero length. CP/M will
then give control to the program at the beginning of the
TPA (100H) and, in effect, the old program will have been
reexecuted. It is desirable to place the command at or
near the beginning of the directory to save search time by
CP/M. Also, the user should be aware of programs which oper¬
ate erroneously when reexecuted, such as the SAVEUSER
command under CP/M on Micropolis and CP/M on Vector MZ.
In order to get the CCP to load a .COM file without execut¬
ing it, you must cause it to issue an error message while pro¬
cessing your command line. This is done by imbedding a
control character in the data field after the program name as
follows:
FILE "A <CR>
Note : Any control character not used by the CCP’s line input
routine are considered illegal and will remain imbedded in the
command line, causing the desired error to occur. In this case
the program FILE.COM will be loaded into ttie TPA. However,
when CP/M scans the data field to set up the twp default
FCB’s, it discovers an illegal character and issues an error
message (a “?”). The program can be executed when desired
by using the command discussed above. This is generally
more useful for single drive systems, but sometimes comes in
handy in two drive systems also.
The program listing below is a non -trivial CP/M command
called “60.” This performs a function which is useful when
no monitor or front panel is available. The program will exe¬
cute the address specified by the four hex digits in the data
field. Spaces are considered to be zeroes.
I hope the preceding is useful to some of the CP/M users
who read DDJ. I enjoy the useful content of this magazine
and hope it continues in the future. Finally, if there are any
usrs of CP/M Micropolis or Vector MZ who have programs
they would like to trade, I would appreciate hearing from
them.
Page 16
Dr. Dobb's Journal of Co mputer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
11
Number 41
12
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 17
10010000110000215I0004047EFE20C210013E307?
10011000C01101D82305C20801EIE8EICD2801D8?E
l0012000292?2?2VB54FEICm30D8FE0A3FDOI688
0801300007FE0AD8FE103FC9CA
0000000000
Linking CP/M To
George Morrows
Cassette Interface
BY WAYNE MILLER
905 Fairmount Blvd.
Jefferson City, MO 65101
I have found that maintaining compatibility with others is
ideal for exchanging software; however, I have had problems
since I acquired a double density minidisk system. Therefore,
I decided to link a cassette interface to CF/M, allowing me to
exchange software with others even if the}/ do not have disk.
I decided on the Speakeasy by George Morrow because it
used the KC300 baud standard. This is very slow; but the
chances of losing data from bit drop-out is very unlikely.
I accepted the drawbacks of the slow speed since I would
only use the cassette to read the program tc> disk.
I am presenting this program primarily as an example to
others to use when writing software to transfer data from a
disk to a cassette tape.
The functions that effect a data transfer have been coded
in a structured format, which should make it wasy to follow,
'rhe reader, however, will need to consult the CP/M and
Speakeasy manuals to get the full description of the disk
and tape functions.
To change the direction of the transfer, the order of read¬
ing/writing the tape and disk will need to be reversed. I have
marked the areas in the program listing for Ihe reader’s benefit.
Note that I transfer a sector at a time. This could be easily
changed if block transfers are desired. Also, there are two
possible disk errors. A # 1 error is caused when the program
tries to open a nonexisting file. A #2 error occurs when
a disk write exceeds available disk space or the disk is in a
'vrite protect mode. If such an error occurs, the message
generated by my program will have the following format:
“# - DISK I/O ERROR ON FIDOS”.
CP/P, TO GEOhGE POhhOVS CASSETTE INTERFACE
SOFTWARE LINKAGE
WAYNE KILLEh
;
905 FAIhKOUNT bLVL•
\
JLFFLhSON CITY# KO* 6510
#
i
FAY 1979
OKG
lOOh
bLOS
LQU
0005hl LNThY POINT TO CP/K
CASSLT
tQU
61 OAh 5 COPL TAPL SYS ILF.
ChLATL
LGU
22; LOS ChLATL FILL
CLOSL
LQU
16; CLOSL ThL FILL
WhITL
LQU
21; LOS WhITL hLCOhL
TAPLF
LQU
202Q 5 TAPL hLAL COKKANL
OPLNF
LQU
15; OPLN FILL COLL
hLALF
LGU
20; hLAL FILL COLL
PhlNTF
LQU
9; PhINT ON CONSOLL
TYPLF
LQU
2; TYPL ON CONSOLL
CON IN
LQU
15 hLAL F hOK CONSOLL
FCb
LQU
05Ch5 FILL CONThOL bLOCh ALLhLSS
BUFF
LQU
fcOhi LISK LF.A bUFFLh
; bLOb
HLGISTLhS hLTUhN VALULS IN A ANU b
;
FUNCTION hLG• IN C
1
FOhWAhL VALULS IN L ANL L
LM
h#0
LAU
SP
ShLL
OLLSP
LX I
SP#SThTOP
KVI
A# *0 *
STA
IBP
JKP
FAIN
IBP
US
1 5 SLCTOh COUNTLh
OLLSP
DS
2
STACK
LS
64
SThTOP
LQU
S
; PhINT ChAhACTLh hOOUNt
PChAh
PUSh h!
PUSh L! PUSh b ; SAVL hLGISTLhS
KVI
C# TYPLF
KOV
L# A
bLOS
b! POP LI POP h JhESTOhE
i TO ThE CALLEP.
TINE TO PEINT bUFFEh ON CONSOLE
H! PUSh D! PUSh EJ SAVE
C.PhINTF
bLOS
bl POP LI POP hi EESTOhEL
ChLF
i TO ThE CALLEh
TINE TO PERFORK LISK I/O
hi PUSh LI PUSh bi SAVE
bLOS
bl POP L! POP hi hESTOhE
TINE TO PEhFOhK TAPE I/O
h! PUSh LI PUSh bi SAVE
CASSET
bl POP LI POP hi hESOhEL
TINE TO SENL CAKfilAGE hETUhN ANL LINE FEEL
A>0Lh
PChAh
A.OAh
PChAh
TINE PERFOhPS LOW LEVEL EhhOh ANALYSIS
ChLF
A # * # '
PChAh
A#b
•O’
PCHAH
Page 18
Dr. Dobb's Journal of Computer Calisthenics 8< Orthodontia, Box E, Menlo Park, CA 94025
Number 41
13
CALL
CRLF
LXI
D#MSG3
CALL
P.'il OUT
JMP
FINIS
MAIN
LX I
D*MSG6
CALL
PFiIOUT
IN
40h
*
AN I
200Q
JZ
MAIN
CALL
SETUP
LX I
b» MSG 1
CALL
PRIOUT
MV I
A* ' $ *
STA
DLLIM
LX I
h» F CB
CALL
PRIOUT
CALL
CRLF
GLOOP
IN
OF FB ; GET SEGMENTS LIMITS
MOV
B*A
LDA
IBP ; DONE
CMP
b
JZ
finis ;yls
LDA
ibp ;no
INR
a
STA
IBP
CALL
CRLF
LDA
IBP
CALL
PCHAR
MV I
A,TAPtFf- ch ange to read or
° WRITE FROM DISK ADD TAPE
D*126 i
LX I
FwOfcOh v*
CALL
TAPLOP^) I
CALL
DISK ^ J
LX I
D*MSG4
CALL
PRIOUT
JMP
GLOOP
FINIS
LX I
D#MSG2
CALL
PhiOUT
LX I
L/FCb
MV I
C w CLOSE
CALL
F1LE0P
LULL
OLDSP
SPFiL
JMP
Oh
MSG1
DB
’ CASSETTE TO LISK ROUTINE S*
MSG 2
DB
' END OF JOB
*
MSG 3
DB
* LISK I/O EhhOR ON bDOS i*
MSG A
LB
’ TRANSFEh FROM CASSETTE COMPLETE S’
MSG 6
DB
' PRESS ANY hEY TO RUN S*
SETUP
LX I
D# FCB
MV I
C>CREATE^- QPEI.
CALL
FILEOP
CPI
2SS
JNZ
OPNOK
MV I
h, 1
CALL
ERR
0PN0K
XP.A
A
STA
FCBCR
RET
DISK
PUSH H!
PUSh D! PUSh b
LX I
D,FCb
MV I
C.kihniL < - OR READ
CALL
BDOS
POP B!
POP D! POP h
CPI
0
RZ
CPI
1
JZ
FINIS
MV I
B#2
CALL
EKh
FCbLN
LQU
FCB+O
FCBFN
LQU
FCB+1
FCbFT
LQU
FCB + 9
FCBRL
LQU
FCb+1 2
FCbl 3
LQU
FCb+13
FCB14
LQU
FCb+14
FCbRC
LQU
FCB+1 b
F CbCF.
LQU
FCB+32
FbbLN
LQU
FCB*33
DLLIM
LQU
FCb+34
LNL
I STOP hUN
*
Number 41
14
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 19
Implementing a tiny interpreter
with a CP/M flavored C
BY LES HANCOCK
Software Products Group
Yourdon Inc.
1133 Sixth Avenue
New York, N.Y. 10036
CP/M users finally have a compiler for the C language.
It’s a subset of the C defined at Bell Labs, 1 but a full and
proper subset, perfectly adequate for most systems’ work. It
was written by Leon Zolman, alias BD Software. Although he in¬
troduces the compiler as an “educational tool” in his user’s
manual, I know at least one software designer who’s making
serious professional use of it already. This article shows
how it can be used as an implementation language on the
8080/Z80.
Last summer was quite a compiler season: a copy of the
BDS ccompiler came to me for pre -release testing a few days
before I was due to leave for the Denver SIGPLAN symposium
on computer construction. The obvious thing to do was to pick
up some hot tips in Denver, then test Zolman’s C by using it
to implement a simple compiler. I believe it was just after
coffee break on the first morning of the symposium, while
Kari-Jouko Raiha was explaining Dynamic Allocation of
Space for Attribute Instances in Multi-Pais Evaluators of
Attribute Grammars, that I began to rethink this plan. What
I finally did write wasn’t a compiler, it was an interpreter
almost as tiny as my humbled ego. Maybe the results will be
interesting to those of you who (like me) are: less than expert
at language implementation. At any rate the interpreter puts
BDS C on its mettle.
My first job was to specify the language. It’s best to do this
by building an LALR(l) grammar that can be elaborated into
a parser. But I cut my teeth on comic books, not on syntactic
structures, so I had to make do with a list of rules:
• A program consists of one or more lines, each ending in a
newline or an end-of-file mark. Any line may begin with a
label.
• The character set of the language includes the usual nu¬
merals and letters (upper and lower case), plus the special
characters.
+ -/ *: ??! ■ ' '<>•€>
These symbols are used to represent tokens which fall into
six categories: identifiers, labels, constants, strings, operators,
and keywords.
• Identifiers (variable names) are single lower-case letters.
They may be assigned numeric values.
• Labels (line labels) are single upper-case letters. They may
not be assigned values by the programmer.
• Constants are signed integers from -32768 through 32767.
• Anything inside a pair of double quotes is a string.
• The operators take action on their operands. An operand
may be a label, an identifier or a constant. The operators
are:
+ - * / the usual arithmetic operators
= assignment
== < > <= >= <> relational operators; if the result
is true the value returned is 1, else
0
; prints its argument
: prints argument on a new line
-> A branches to line labeled A
“ ” encloses a string
opens a comment
closes a comment
° The keywords provoke events but do not take operands.
They are:
| EEE J SSS if-then: if expression EEE is
evaluated to nonzero, executes
the statement SSS, which may
contain another if-then
? waits for numeric input from
user’s console
! halts execution
• Expressions are evaluated right to left. (But note that the
if-then construction proceeds from left to right, though the
expression in each if-clause is evaluated right to left.)
• Blanks and comments are ignored unless they occur in
strings.
• The operators -> : ; and the keyword ! terminate
evaluation of a statement.
• Only integer variables are permitted.
• Comments nest.
Page 20
Or. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
15
Now we know as much about the target language as the
interpreter does, so we should be able to interpret a program
ourselves. Let’s try this one:
A 5 ‘enter a number (0 to stop)'
-C 0 == x = ? > !
i ‘its souare is *
t X * X
-> A
We can easily execute it by eye. The first line, labeled A,
prints a string that tells the user what to enter. The second line
contains an if-then construction. Evaluating the if clause right
to left, we begin with the keyword ?, which gets a number
from the user’s console. The = operator assigns that value to
the identifier x. The == operator compares the value of x with
the constant 0. If this comparison works — in other words, if
the user entered a zero — the result of the expression is 1,
which causes the then statement to be executed. That state¬
ment consists of the keyword !, which halts the program. But
if x is anything except 0 the comparison fails and the program
continues on to the next line, printing “its square is’’followed
by the value of x multiplied by itself. In the last line the - >
operator causes control to pass back to the line which begins
with A.
The interpreter works by doing exactly what we’ve just
done: scan a line, evaluate it, scan another line, evaluate that,
and so on. Scanning means reading the symbols and recogniz¬
ing the tokens they stand for. Some tokens can be recognized
immediately: + always denotes the ADD operator, x an
identifier, X a label. Others take more analysis. For example,
when scanning turns up the symbol - the token it represents
may be SUB (for subtraction) or NEC (negation). The - may
even be half of the GOTO symbol ->. Context tells us what’s
what: if the - symbol immediately follows an operator the
token must be NEG; if it’s followed by a > the token is
GOTO; if it follows an identifier or constant and precedes
another identifier or constant, the token has to be SUB. Once
all the tokens in a given line have been recognized, the line can
be evaluated by following the rules of action set up for each
operator and keyword.
So the interpreter needs two main moving parts, a scanner
and an evaluator. A prescanner would be nice too — it could
strip out blanks and comments and make the source code
more compact.
That’s exactly how the interpreter was designed. Its driving
function begins by calling out the prescanner, which filters
the ASCII input file and pours the results into the program
buffer. Then the scanner and evaluator are called to process
the filtered code. The scanner gets the next token from the
program buffer and disposes of it in one of six possible ways:
1. operators go into an operator stack
2. constants go into a value stack
3. labels are copied from the symbol table into the value stack
4. identifiers (variable names) are copied from the symbol table
into the value stack; if an identifier isn’t yet in the symbol
table, the scanner puts it there
5. strings go into a string buffer; an entry in the value stack points
to each string
6. keywords are dealt with immediately.
The evaluator never sees the ASCII symbols in the program
buffer. Its job is to evaluate a single line on the basis of the
tokens it finds in the operator stack, value stack, symbol table
and string buffer. It pops operators and values from their
respective stacks and handles them according to the rules that
define the tiny language.
Before looking at the C functions that run the interpreter
we’d better understand its four data structures in more detail.
The program buffer is a character array that contains the
program’s ASCII source code as filtered through the prescan¬
ner. Here’s how the square-your-number program looks in its
buffer:
J'enter a nu»ber <0 to stop)'\n-C0*=x»?>!\nJ'
its souare is *\n?x*x\n->A
Note that the carriage-retum/linefeeds have been replaced
by the C newline (represented here in conventional C notation
as In) and that the initial line label A has disappeared into the
symbol table, where it’s equipped with a pointer aimed at the
first character in the program buffer. Incidentally, the last
character in the buffer is always a CP/M end-of-file (Oxla),
not shown in the example.
The symbol table contains one entry for every label or id en¬
tifier encountered in the process of scanning (or prescanning)
the source code. The symbol table symtab is an array of
structures each of which contains a one-character symbol and
its associated value, either an integer (for identifiers) or a
pointer to the head of some line in the program buffer (for
line labels):
symbols <
char symbol* /* l.c. for IDENT* u.c. for LABEL */
union <
int integer* /% if ident is IDENT */
char ilinef /* if ident is LABEL */
> auidf
> symtabCSTAKSIZED * *symptrJ
The symbol table pointer symptr will always point to the
next available element of symtab.
Unlike the other data structures, the symbol table never
shrinks; it can grow as the scanner finds new symbols, and its
integer component can change as variables get new values, but
nothing’s ever elided. The operator stack, value stack and
string buffer are rebuilt from scratch every time a line (or an
if-clause or a then-clause) is scanned.
The value stash is an array of structures topped off bv a
stack pointer — tokens may be pushed onto it or popped off it
by incrementing or decrementing valsptr. In the first draft of
the interpreter this data structure was called operandstack,
which is more exact than valuestack but too easy to confuse
with operatorstack, its opposite number. At any rate, the
structures look like this:
values <
int taper /* naa be IDENTr LABELr CONSTANTr STRING »/
union <
SYMBOLS #ptrsanif /% if type is IDENT or LABEL */
char tsubstrind* /* if type is STRING */
> auod*
int value* /* if type is IDENT or CONSTANT */
> valuestackCSTAKSIZEJ* *valsptri
The type of an entry determines which if any of quod's
members are useful. When an operand is an identifier or a Line
label quod's value is ptrsym, a pointer to the appropriate sym¬
bol table entry. When it’s a string quod's value is substring,
a pointer to the string’s location in the array strings. For
constants quod has no use at all.
Number 41
16
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Me nlo Park, CA 94025
Page 21
Where operands have a numeric value an entry is made in
value, which otherwise contains garbage. 2
The operator stack is just an integer array with a stack
pointer:
int operstorstackCSTAKSIZEJ r #oPSPtrf
Every operator that can go into the stack has a numeric code:
ASCII
symbol
mnemonic
code
comments
+
PLUS
1
-
MINUS
2
*
TIMES
3
/
DIV
4
=
GETS
5
assignment
PRINT
6
piint with newline
»
PRT
7
piint sans newline
->
GOTO
8
==
EQ
9
logical equivalence
>
GT
10
greater than
>=
GE
11
greater than or
<
LT
12
equal to
less than
<=
LE
13
less than or equal to
<>
NE
14
logical inequality
The numbers can be anything so long as there’s no duplication.
The string buffer is the simplest of all the data structures:
char strinasCLINED r #strptr»
As strings are encountered in the scan they go into strings.
The pointer strptr always indicates the next available element
in this array.
So much for the data structures used to implement the in¬
terpreter. You may have noticed that each one is associated
with a pointer. Like most other up-to-date implementation
languages, C leans heavily on pointers and recursion. We’ll
come to the recursion now as we look at the interpreter’s
main functional modules, main, prescan, scan and evaluate,
main is the driving function. It follows this outline:
initialize stop/go flag, bugger pointer, symbol table pointer
prompt for input file name
prescan the file
if no errors so far,
reinitialize buffer pointer
while the stop/go flag is GREEN,
clear the value stack
clear the operator stack
clear the string buffer
move the scanner through the program buffer till it
hits the end of the current line or the end of the
buffer, or encounters a STOP or an error
if the scanner has reached the end of the buffer, set the stop/
go flag to RED
call the evaluator
prescan opens the input file and calls the supporing func¬
tion readchar to get new characters in sequence until end-of-
file is reached, readchar is delegated the job of ignoring com¬
ments and linefeeds. Linefeeds are easy enough, but we’ve
stipulated that comments nest. A global counter called incom¬
ment is used to keep track of how deeply we’re nested in
comments at any given moment. There are two kinds of com¬
ment tokens, LCOMMENT (to open the comment) and
RCOMMENT (to close it), readchar follows this strategy:
get the next non-LINEFEED character from the file if it’s an LCOM¬
MENT,
increment incomment
else if it’s an RCOMMENT,
decrement incomment
if incomment is nonzero or if the character’s an RCOMMENT,
call readchar recursively
else return the character
Recursion provides a neat solution to the nesting problem.
prescan itself has the job of eliminating blanks and of
putting labels into the symbol table. Since blanks in strings
must be preserved, the local variable instring is used as a flag.
Strings don’t nest, so instring need take only two possible
values, YES and NO. prescan’s internals aren’t very interesting.
When it finds an upper case alphabetic character at the head
of a line it assumes it has a label and installs the character
in the symbol table along with the current value of the pro¬
gram buffer pointer. Since the labels are no longer needed in
the source code, they’re not read into the program buffer. All
other characters, including labels which don’t occur at the
head of a line, do go in.
scan is the biggest and trickiest function of the lot—too
big, really. Its argument is an ASCII character from the pro¬
gram buffer. A long series of case statements are used to recog¬
nize the argument as a keyword or as an operator (or as the
first character of an operator’s symbol); if that fails, it should
be an operand. Most of the operators get minimal processing:
things like PLUS or TIMES or DIV simply go onto the opera¬
tor stack. But the keywords are handled entirely by the
scanner, and one of them, IF, exercises scan to its fullest.
Consider the if-then construction as a whole. Where we
have a line like
•C 0 == x = ? > !
we want to parse and evaluate the conditional clause before
going on to parse and evaluate the statement that will be
executed if the condition is true. This calls for recursion.
Look at the ‘ | ’ case of scan in the C source code. When scan
meets this symbol, it clears the value stack and the operator
stack and calls itself just as it gets called in main. Successive
characters are scanned until the matching ‘) ’ is reached.
The effect of the ‘ J ’ case is simply to return a zero, which is
the signal scan uses to tell its calling function that it’s reached
a stopping place. At this point control passes back to the first
invocation of scan, which checks to be sure that a ‘ J ’ is in
fact what stopped the scanning process. If so, it calls evaluate
to evaluate the part of the line just scanned—that is, the part
inside the if-clause. The function evaluate returns the numeric
result of its evaulation. Should that result be nonzero, scan
clears the stacks again and returns 1, which tells the call¬
ing function to go ahead and finish scanning the current line.
If the result is zero, scan pushes bufptr ahead to the next
newline, skipping the statement following the THEN. In this
little recursive drama scan briefly plays the part of main. 3
Recognizing operands is a fairly straightforward business.
Except in strings, an upper case letter must be a label, a lower
Page 22
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
17
case letter must be an identifier, and a digit can only be part
of an integer constant. Since labels at the head of a line have
already been dealt with by the prescanner, the scanner should
find labels only after GOTOs. Whenever a GOTO turns up we
peek ahead one character to be sure there’s a label coming: as
soon as we reach the label we look back one character to be
sure we had a GOTO.
When the scanner encounters a label it calls idlookup
to see whether the label’s in the symbol table. If not, that’s
an error. Otherwise an entry is made in the value stack, setting
the type to LABEL and setting quod.ptrsym to point to the
label’s symbol table entry.
The story’s somewhat different for identifiers. It’s per¬
fectly OK to find that an identifier is not yet in the symbol
table. When that happens the scanner calls idinstall to put it
there. The entry made in the value stack will have a type
of IDENT, a quod.ptrsym pointing to the symbol table entry,
and a value equal to whatever was contained in the symbol
table’s integer field.
When the scanner meets a constant it accumulates the con-
sant’s integer value with the help of the library routine atoi?
This goes into the value stack’s value member, with the type
set to CONSTANT. Negative numbers are accumulated by a
recursive call from the - case.
Eventually we scan up to a newline, at which point main
passes control on the evaluate. Though it’s fairly long, evaluate
is a simple function. If it sees a RED flag it simply returns,
leaving main to stop the program. Otherwise it pops the oper¬
ator stack once and the value stack twice. If either stack is
empty, evaluation is finished. If not, evaluate goes to the case
statement that matches the operator and carries out the
action it finds there. Most operators are binary-that is, they
take two operands. All binary operators do essentially the
same thing: they combine the two operands in some way
(add them, divide them, compare them), then put the result
back onto the value stack as a CONSTANT. One binary oper¬
ator, GETS, stands apart. Its left operand must be of type
IDENT. Otherwise it’s like any other binary operator, which
makes expressions like
0 == x = ?
perfectly legal.
The unary operators are PRINT, PRT and GOTO. One of
the rules we used to define the language being interpreted
was that these operators terminate execution of a statement.
In fact they jump right out of the evaluator, using C’s own
goto. There are nicer ways to do this—for example, by setting
a local flag to be checked in the while- but I did want to
wring out the compiler, and I’ve always had a salacious yen to
use C’s goto.
The interpreter’s GOTO operator works by setting the pro¬
gram buffer pointer to the address recorded in the label’s
symbol table entry. When evaluate ends, main tells scan to
start scanning the line that begins at that address. It’s very
much like the 8080 jump instruction, which loads the jump
address into the program counter.
Examples are included here to show how BDS C compiles
and runs the tiny interpreter, ccl and cc2 are the two halves
of the compiler. They generate relocatable object files which
clink links with libraries to produce absolute 8080 code.
According to Leor Zolman, his C trades object code ef¬
ficiency at runtime for structure and clarity during program
Number 41 Dr. Dobb's Journal of Calisthenics &
18
development. This is certainly true in a sense—the interpreter’s
.COM file size is 12K bytes-but memory’s cheap these days,
and as for time, I hate to think how long it would’ve taken me
to code this interpreter in 8080 mnemonics. Where speed and
space are really critical, C can be used to prove the logic of
a system which will eventually be written in assembler.
The BDS C compiler, with libraries, linking loader and good
documentation, is available from tiny C associates (201/
671 -2296) and Lifeboat Associates (212/580-0082) for about
a hundred dollars. I recommend it.
Author's Self-Portrait
Footnotes
(1) The best definition is Appendix A of Brian W. Kemighan and
Dennis M. Ritchie, The C Programming Language, (Prentice-Hall,
1978).
(2) I know: value could go into quod. There’s a reason I chose not to
do that, but I can’t remember what it was. Also: why quod and not
another quid'! It’s one of the BDS compiler’s few serious restric¬
tions. To quote the user’s manual, “Names of members and tags in
the structure definitions cannot be the same as any regular local
variable names, nor can more than one structure or union per
function use a given identfier as a member or tag name.”
(3) See line 18 of the test program 16.tst for an example of deeper
recursion in if-then’s.
(4) Zolman provides the usual C runtime routines, plus quite a few
useful library functions.
listing
B. type x. c
/***********************
## Tiny interpreter t version of 10/23/1979.
## by Les Hancock
** New Yor< City
**
** Operators 35 follows.
**
** + - / * as usual
#* > >= < <= <>'also as usual
## ? prints its argument* then a newline
*# i prints its argument sans newline
## ->A branches to line label A
**
#* Keywords?
#*
#* ? prompts for numeric input
## ! halts execution
-C expression > statement executes statement
## if expression is evaluated to nonzero
Orthodontia, Box E, Mnnlo Park, CA 94025 Page 23
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
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Number 41
Dr. Dobb s Journal of Calisthenics & Orthodontia. Box E Menlo Park, CA 94025
Page 25
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Number 41
22
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 27
your move
error
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
23
whose turn?
ALS-8 to CP/M
File Converter
BY HOLLIS FRAMPTON
SUNY - Center for Media Study
Buffalo, New York 14214
This routine may be administered to alleviate pain. We can’t
be the only people who are making the transition from ALS-8
and its various cousins (Software Package # 1, et al.) to CP/M.
There’s enough work in interfacing a library to the utilities of
a new operating system, without battling the discrepancies
between file formats as well. Reasoning that some drudgery
is too grim even for system programmers, and faced with the
transfer of some hundreds of files to the new system, I wrote
CPCON and would like to share it.
With several embellishments, it runs in 1085 bytes plus
24 bytes worst case for the stack, and on a Sol-20 running
at not quite 2 MHz converts itself in about 2 l A seconds;
about half this time is taken up by two special passes through
the ALS-8 source file to handle the special case of the quoted
ASCII blank (as in MVI A,’ ’). A few redundancies allow
some of the bells and whistles to be detached with ease: a
couple of these are documented in the preamble to the listing.
Some seeming software overkill (the recurrent MVI A, — 1)
deals with bizarre special cases in source files. They are there to
“bullet-proof’ the code, so remove them at your peril. If it
seems over-commented, it is: I love to play the ‘you-figure -
it-out’ game with other people’s code, but not with my own
... 3 days later.
A word about constraints. Our ALS-8 is the PROM version,
resident from E000-FFFF hex. We’re running CP/M on North
Star minifloppies, with a bootload PROM at E900 and a
Thinkertoys DISCUS with PROM at E000. Hence the pain¬
fully slow strategy of dumping to tape. Those with more
flexible memory maps, if they can arrange to have ALS-8,
CUTER and the BDOS part of CP/M simultaneously resident,
will of course want to automate the whole procedure. Since
both SOLOS and CUTER return tape header data in known
Number 41
24
RAM areas, it’s a trivial matter to have CP/M perform auto¬
matic disk saves from tape files read in under the SOLOS/
CUTER utilities. Equates in CPCON adhere strictly to the
widely published labels in documentation for both SOLOS/
CUTER and ALS -8.
The VDM output driver is a CRT driver that uses the
VDM-1, a memory -mapped display, but partially simulates a
terminal, conventionally blanking the screen and cursor on
receiving ctrl-S and Ctrl- A respectively. Presumably the CP/M
source file conventions will be known to anyone desiring to
use CPCON; for ihose who wish to patch it for other source
files than those native to ALS-8, the specs are as follows. A
line consists of: (1) a ‘character count’ byte. The count tal¬
lies all characters in the line, plus the terminating CR, plus
itself -, (2) Zero or more printable ASCII characters; and (3)
a CR (not a CRI.F). Meaningful data begins in column 6 of
an assembler source file, with a blank separating it from a
4-digit decimal line number. Labels may or may not be fol¬
lowed by a colon; in either case the label field terminates
with a blank. Labels are considered unique to 5 characters,
but may contain 6; CPCON disregards label length. Opcode
and operand fields terminate with blanks and may contain
no imbedded blanks. The ALS-8 output formatter requires
a dot as a dummy operand to pretty-print after RET, PCHL,
XCHG and so on. Comment fields are separated by at least
one blank from the preceding field, pretty-print with 2
blanks, and tolerate a leading semicolon or asterisk delimiter.
Comment lines may be indicated only by a leading asterisk.
Does that sum it up? It’s hard to remember: the ALS-8
assembler supports some fairly baroque ambiguities, dating
perhaps from the days of the 4004 or the 2002 orlOOl.
Handling of string constants is summarized on the preamble.
Page 29
Dr. Dobb’s Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Dear Suzanne,
Here’s a fresh listing of CPCON, which converts
resident source of text files in ALS-8 (SPKG1) format
to CP/M format. The routine will accept anything
the ALS-8 assembler finds edible, and produce an out¬
put file equivalent to a CP/M *.PRN file from ASM.
COM or MAC.COM but stripped of its first 16 columns.
All labels emerge followed by colons; semicolons pre¬
cede comment lines and fields; tabs are appropriately
inserted. The ASC pseudo-op is converted to a DB,
and all ambiguities in its argument string are resolved
to single-quote delimiters. ALS-8’s directives COM,
LIST and NLST are left undisturbed; tie feature that
packed them out was removed when a fils written under
the ALS-8 video editor suffered deletion of a macro
call to something named LIST. Hand checking is urged
for these cases.
Users who aren’t in the habit of quoting ASCII blanks
(20H) may shorten the routine by two entire passes,
by deleting lines 94-106, line 141 (CALL SPFIX)
and SPFIX itself (lines 404-412). Yet .mother pass is
taken to convert comment fields in statement lines to
lowercase: disable the option by deleting the CALL
LCASE at line 142, and the apposite subroutine at lines
414-460. With all options enabled, CPCON reformats
itself (about 24K) in less than 2 seconds. It then saves
the reformatted file twice to tape, and offers to display
the reformatted file at the console (tabs are not expand¬
ed). The very nervous, wishing more than one verifica¬
tion, should enter via a CALL to CCOPY; the confident
may delete the option and shorten the code by omitting
lines 150-167 and all of MSSG4.
Two idiosyncrasies should be noted. Fust: comment
fields in statement lines, once detected (and proved not
‘empty’) are passed intact to the reformatted output.
An earlier version deleted leading blanks, and succeeded
in trashing most of what was intelligible in a banner
headline routine that depended on a large table. Those
who wish to pack out leading blanks in comment fields
can insert an appropriate test in TSTCF or TSCF1.
Second: the command switch in CPCON offers to re¬
format pure text files, a much simpler procedure which
simply removes the “character count byte” (see below),
the line number, and the column thereafter. It has been
our custom to use an ASCII dot (.) as a ‘line holder”
in such text files, since an empty line produces bizarre
(try it!) output from the ALS-8 console TEXT com¬
mand. Accordingly, entry at PTFOR tests for such “line-
holders” and converts them to blanks; more than one
dot is assumed to be part of an ellipsis and is passed
unchanged. Anyone who has used the video text editor
in ALS-8 as a convenient alternative to ED.COM may
experience difficulty with this protocol where they
have written input files for text processors, since most
such software uses leading dots in column 1 to flag a
command. Those wishing to reformat only assembly
language files may make entry at ASFOR... but be
sure you test for a non-existent source file or CPCON
will attempt to reformat all of RAM.
A few notes about system calls and file-structure
assumptions. Those working with the PROM version of
ALS-8, which resides at EOOO-FFFF and SOLOS/
CUTER, those superdreadnoughts of the late Processor
Technology Corp., will be able to use this program as-is.
ALS-8 expects to find RAM at D000-DFFF and stores
the 5 -character name of it’s current file starting at D000
(FNAME). Thereafter, binary pointers to start-of-file
and end-of-file are stored at D005 and D007. As a
convenience, ALS-8 returns the current filename and its
address parameters to the console output driver on entry
at FILE (E5BO) without checking file structure. EORMS
(E060) is the warm entry point to ALS-8 (signs on with
“READY”.) The VDM console output driver (FE77)
accepts a printable character in register B and trashes
the accumulator; a ctrl-Z blanks the screen, assuming
IK of display RAM starting at CCOO. The SOLOS/
CUTER input routine behaves like the specs for CONIN
in CP/M, returning with the zero flag set on no input,
else delivering the character in A. Tape routines in
SOLOS/CUTER assume a header block, starting address
and byte count: patch them for your own drivers ad lib.
The persent version dumps formatted files to tape at
1200 baud, in CUTS format, under the filename known
to ALS-8 and typed “A” or “T”.
For those who have not undergone the pain of
working with the ALS-8/SPKG1 format, this is it. Files
are line- oriented and line-numbered. A formal line
consists of 1 -65 lines (there’s a terminal-width switch in
command mode, but EDIT truncates all lines on exit).
Each line consists of: (1) a “character count” byte. The
count of characters in the line includes itself ; (2) a
4-character ASCII decimal line number; (3) a dummy
character, normally a blank, ignored by the assembler;
(4) a string of printables; (5) an ASCII carriage return
(CR: = ODH), the end-of-line marker. Thus an empty
line contains only a “character count” byte, which
evaluates to a binary 1 (that is itself). Therefore hex 01
is the end-of-file character. The far simpler CP/M file
structure assumes no line numbers, inserts a CR and a
LF after each line, and posts an arbitrary ctrl-Z as an
end-of-file mark on all but *.COM files. Incomplete
pages under CP/M are filled with ctrl-Z, a convention to
which CPCON conforms.
CPCON was built for systems (514” North Star and
8” Thinkertoys) whose boot load PROMs overlap the
ALS-8 address space. Hence the download to tape.
Then change circuit boards, and read back the tape files
under SOLOS/CUTER. The tape loader returns a hexa¬
decimal filesize parameter: convert it to decimal and
call it “bb”. Warmboot CP/M and type “SAVE bb
FILENAME.TYP” and CR. It’s a lot easier if CP/M and
your version of ALS-8/SPKG1 and SOLOS/CUTER
can be made co-resident, but ours can’t, so we didn’t
bother to write it that way. No trouble about asking
CP/M to pick up the parameters, build a new FCB
(file control block), and autosave the source: see the
manual “CP/M Interface Guide,” a model of lucidity
which allows the programmer to treat an operating
system like a device with a few control ports.
Regards,
Hollis Frampton Digital Arts Lab
Ps ge 30
Dr. Dobb's Journal of Computar Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
25
Converter!
Listing |
0000 ************************************************
0001 * *
0002 * CPCON.ASM: AN ALS-8 TO CP/M FILE CONVERTER *
0003 * *
000A ************************************************
0005 *
0006 * CONSTANTS
0007
*
0008
CP. s
EQU
0DH
0009
CTRLZ:
ECU
1 AH
;CP/M EOF
00 10
ESC:
EQU
1BH
/'PANIC BUTTON
001 1
ETX:
EQU
3
00 12
FILL:
EQU
0
/'DUMMY BYTE FOR * * CASE
00 13
LF:
EQU
0AH
00 1 4
QUOTE:
EQU
27H
/'ASCII <’>
001 5
TAB:
EQU
09H
/'ASCII <HT>
0016
*
0017
* SOLOS/CUTER
EQUATES
0018
*
00 19
BLOCK:
EQU
0C823H
0020
FNUMF:
EQU
0C854H
0021
HTYPE:
EQU
0C822H
ITYPE BYTE IN SOLOS TAPE HEADER
0022
LOADR:
EQU
0C825H
0023
SINP:
ECU
0C01FH
5 SOLOS SYSTEM INPUT DRIVER
0024
THEAD:
EQU
0C81CH
0025
UNIT1:
EQU
80H
0026
VTAPE:
EQU
0C77FH
0027
*
0028
* ALS-
8 ECUATES
0029
*
0030
BOFP:
EQU
0D005H
/•BEGINNING-OF-FILE POINTER
003 1
EOF:
EQU
0 I H
/ALS-8 END-OF-FILE MARK
0032
EOFP:
EQU
BOFP+2
;END-OF-FILE POINTER
0033
EORMS:
ECU
0E060H
5ALS-8 SIGN-ON ENTRY PT
0034
FILE:
EQU
0E5B0H
;RETURNS CURRENT FILE PARMS
0035
FNAME:
ECU
0D000H
/•CURPENT FILE NAME
0036
VDM:
EQU
0FE77H
;ALS-8 CPT OUTPUT DRIVER
0037
0038
*
ORG
1 00H
/•PUT IT VHEPE YOU WANT IT
0039
*
0040
CPCON:
LXI
H/0
/'CLEAR TO RECEIVE...
004 1
DAD
SP
;...CALLING SP
0042
SHLD
SYSSP
/•SAVE IT
0043
LXI
SP/STACK /-FOPCE PROGRAM STACK
0044
LHLD
BOFP
;get stapt of file ptr
0045
MOV
A/M
;get fipst char
0046
CPI
EOF
/•FILE EMPTY?
0047
JZ
ERROR
;AB0RT 4 REPOPT
0048
STA
CCBYT
;else save character count byte
0049
SHLD
LI NAD
;start addp of current line
00 50
SHLD
DEST
/•DEST FOP NEW SOURCE FILE
0051
CALL
GTSRC
/‘FIND START OF NEXT SOURCE LINE
0052
BEGIN:
MVI
B/CTRLZ
/•BLANK SCPEEN
0053
CALL
VDM
0054
LXI
H/MSSG2
/•POINT TO MESSAGE
0055
CALL
VDPRT
/4 SIGN ON
0056
INPUT:
CALL
SINP
t LOOK FOR KEY PRESSED
0057
JZ
INPUT
/•NONE/LOOK AGAIN
0058
CPI
ESC
/•RETURN TO ALS-8?
0059
JZ
RETRN
;back to system
0060
CPI
•T*
/•TEXT?
0061
JZ
PTFOR
/•GO FORMAT PURE TEXT FILE
0062
CPI
•A*
/•ASSEMBLY LANGUAGE FILE?
0063
JZ
ASFOR
/'A DIFFERENT KETTLE OF FISH
0064
0065
*
JMP
BEGIN
;else operatop error
0066
PTFOF: LHLD
SOURC
z*HL = SOURCE FILE PTR
0067
XCHCi
.
IDE = SOURCE FILE PTR
0068
LHLI)
DEST
JHL = DEST FILE PTR
0069
LDAX
D
/'GET SOURCE CHAP
0070
CPI
• . •
/‘POSSIBLE TEXT "LINE HOLDER"?
0071
JNZ
PTFRI
/•NO/IT’S A NORMAL LINE
0072
I NX
D
;POINT TO NEXT SOURCE CHAP
0073
LDAX
D
/•AND FETCH IT
0074
CFI
• . *
/•PROBABLE ELLIPSIS?
0075
JZ
PTFF0
IFIP.ST dot was not a LINE holder
0076
MVI
Mz * *
;SUBSTITUTE BLANK FOR DOT
0077
I NX
H
;BUMP DEST PTR
0078
JMP
PTFP1
0079
PTFPP: DCX
D
;REWIND TO START OF NORMAL LINE
0080
PTFRI: CALL
MVRM1
IMOVE TEXT LINE
0081
CALL
GTNXT
;CHECK FOR NEXT LINE
0082
JZ
PTDON
;eof encountered
0083
CALL
GTSRC
;UPDATE SOURCE PTR
0084
JMP
PTFOR
/•PROCESS NEXT LINE
0085
PTD0N: MVI
A/ *T*
;"TEXT" FILE TYPE
0086
STA
HTYPE
;INSERT IN TAPE HEADER
0087
CALL
NDFIL
;ENDFILE 4 FILL BLOCK
0088
JMF
FINIS
/•DISPLAY 4 SAVE
0089
*
0090
ASFOP: LHLD
BOFP
;HL = START OF SOURCE FILE
009 1
ASFP0: MOV
A/M
;get a char
0092
ASFPI: CPI
EOF
/•DONE WITH FIRST PASS?
0093
JZ
ASFP2
;YES/ BEGIN FORMATTING
0094
CPI
QUOTE
;test for start of • * case
0095
JNZ
ASMP1
;not a quoted byte
0096
I NX
H
/•POINT TO QUOTED BYTE
0097
MOV
A/M
J GET IT
0098
CPI
• •
,*IS IT A BLANK?
0099
JNZ
ASMOR
/•SOMETHING ELSE/ MOVE PAST
0100
I NX
H
/•POINT TO POSSIBLE ENDQUOTE
0101
MOV
A/M
;FETCH IT...
0102
CPI
QUOTE
J...4 TEST
0103
JNZ
ASFR1
/'NOT A VALID • • CASE
0104
DCX
H
/'YES/ POINT TO QUOTED BLANK
0105
MVI
M/FILL
/'INSTALL TEMPORARY DUMMY
0106
ASMOR: I NX
H
/'POINT TO CLOSING CUOTE
0107
ASMR1: I NX
H
;POINT TO NEXT CHAR...
0108
JMF
ASFR0
;...4 GO TEST IT
0109
ASFR2: LHLD
SOURC
;PT TO SOURCE BLOCK
01 10
MOD
A/M
/•GET FIRST SOURCE CHAP
01 1 1
CPI
• * •
;IS IT ALS-8 REMARK?
01 12
JNZ
TSTLB
;NO/MUST BE A LABEL
01 13
CALL
MVREM
J MOVE THE REMARK INTACT
01 14
CALL
GTNXT
;UPDATE FORMAL SOURCE LINE ADDR
01 1 5
JZ
NOMOR
/'EOF FLAG RETURNED
01 16
CALL
GTSRC
/•UPDATE PHYSICAL SOURCE LINE A DDR
01 17
JMP
ASFR2
;look at next line
01 18
TSTLB: LHLD
SOURC
;get ptr to physical source LINE
01 19
MOV
A/M
/•GET FIRST CHAR
0120
CPI
• •
I ALPHA HERE FOR LABEL
0121
JZ
DOOPC
;N0 LABEL/ FIND OPCODE
0122
CALL
MVLAB
/•MOVE THE LABEL
0123
DOOPC: CALL
MKTAB
/•FORCE CP/M FORMATTER
0124
CALL
MOVOC
/•NOV MOVE OPCODE FIELD
0125
JZ
NDLIN
/'PREMATURE EOL
0126
CALL
MKTAB
/•INSERT TAB AFTER OPCODE FIELD
0127
CALL
MOVOP
/'MOVE OPERAND FIELD
0128
JZ
NDLIN
/•PREMATURE EOL
0129
CALL
MKTAB
/'INSERT TAB AFTER OPERAND FIELD
0130
CALL
FNDCF
/'FIND COMMENT FIELD
0131
JZ
NDLIN
/•COMMENT NOT PRESENT/ EOL
0132
CALL
MOVCF
/'MOVE COMMENT FIELD
0133
*
0134
NDLIN: CALL
GTNXT
5LINE FINISHED/TEST FOR NEXT
0135
JZ
NOMOR
JEOF ENCOUNTERED
0136
CALL
GTSRC
JCOMPUTE PHYSICAL SOURCE PTR
0137
JMP
ASFR2
/'PROCESS NEXT LINE
0138
NOMOR: MV:
A/ 'A'
/•ASSEMBLY LANGUAGE FILETYPE
0139
STA
HTYPE
/•INSTALL IN SOLOS HEADER
0140
CALL
NDF IL
5MARK EOF 4 FILL BLOCK
0141
CALL
SPFIX
/'CONVERT DUMMIES TO BLANKS
0142
CALL
LCASE
JCONVERT COMMENTS TO LOWERCASE
0143
FINIS: MVI
Bz CTRLZ /'BLANK SCREEN
0144
CALL
VDM
0145 LX I H/MSSG3
0146 CALL VDPRT
0147 CALL FILE ;DISPLAY FNAME & NEW PARMS
0148 CALL TSAVE i ONCE!
0149 CALL TSAVE S TWICE!
0150 LX 1 Hz MSSG4
0151 CALL VDPRT
0152 YESNO: CALL SINP ITEST FOR INPUT
0153 JZ YESNO /'NONE/ LOOK AGAIN
0154 cp: ’y' ;signal to verify file?
0155 JNZ RETRN /'FUNCTION NOT DESIRED
0156 CCOPY: LHLD BOFP /'GET PTR TO START OF FILE
0157 CPCOP: MOV A# M »GET A CHAR
0158 CPt CTRLZ ;END OF CP/M FILE
0159 JZ RETP.N ;YES/ RET TO SYSTEM
0160 CPt TAB JELSE LOOK FOR TAB
0161 JNZ CPOUT ;no, PUBLISH THE CHAR
0162 MV [ Bz ’ • /'SUBSTITUTE SPACE FOR TAB
Number 41
26
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 31
0163
JMP
CPOTI
; DISPLAY IT
0260
INX
H
0164
CPOlTTs
MOV
B* A
;SET THE CHAR UP
0261
MVI
M* • •
J...PSEUDO-OP
0165
CPOTI t
CALL
VDM
J SEND TO CRT
0262
DCX
H
JPOINT TO 'B*
0166
I NX
H
;bump file ptr
0263
DCX
H
JPOINT TO * D*
0167
JMP
CPCOP
;LOOP 4 DO NEXT CHAR
0264
XCHG
.
J DE = SOURCE PTR* HL = DEST PTR
0168
*
0265
MVOCF: LDAX
D
J GET SOURCE CHAR
0169
PETRN:
LHLD
SYSSP
;get back calling sp
0266
CPI
CR
JEND OF OPCODE AND LINE
0170
SPHL
•
;RESTORE
e267
JNZ
MVCFl
J NO EOL* LOOK FOR FIELD DELIM
0171
JMP
EORMS
;back to caller
0268
SHLD
DEST
JUPDATE DEST VARIABLE
0172
*
0269
JMP
LNDON
JTERMINATE OPCODE FIELD
e»73
EFtF.On*
LXX
H# M55G1
0270
MVCFl! CPI
1 *
JEND OF OPCODE?
0174
CALL
VDPRT
0271
JZ
MVDON
JTERMINATE OPCODE FIELD
0175
CALL
FILE
5 SHOW EMPTY FILE PARMS
0272
MOV
M* A
J PUT CHAR TO DEST FILE
0176
JMP
RETRN
0273
INX
D
J BUMP SOURCE...
0177
*
0274
INX
H
J...4 DEST PTRS
0178
GTSRC:
LHLD
LI NAD
;get ptr to formal line
0275
JMP
MVOCF
JCONTINUE OPCODE FIELD MOVE
0179
LXI
D# 6
; FORCE OFFSET
0276
*
0180
DAD
D
; HL a PTR TO PHYSICAL SOURCE LINE
0277
MVDON: SHLD
DEST
JUPDATE DEST VARIABLE
0181
SHLD
SOURC
JSAVE IT
0278
MVDNl: XCHG
.
J HL a NEXT SOURCE ADDR-1
0182
RET
0279
SHLD
SOURC
J SAVE SOURCE PTR
0183
*
0280
*
0184
MVREM:
MV I
m* •; •
;CP/M REMARK
0281
OKRET: MVI
A, -1
JMAKE DEFINITE NON-ZERO
0185
XCH6
•
;DE » PTR TO SOUPCE
0282
ORA
A
JCLEAR ZERO FLAG FOR NO EOL
0186
LHLD
DEST
;HL * PACKED SOURCE DESTINATION
0283
RET
0187
*
0284
*
0188
MVRM1 :
LDAX
D
J GET SOURCE CHAR
0285
LNDON: LHLD
DEST
J GET DEST PTR
0189
CPI
CR
JEOL MARK?
0286
LNDN1 : DCX
H
JPOINT TO LAST PACKED CHAR
0190
JZ
MRDON
; REMARK LINE MOVED
0287
MOV
A*M
J GET IT
0191
MOV
MjA
JMOVE CHAR TO DEST
0288
CPI
TAB
J CP/M FORMATTER?
0192
INX
D
;bump source...
0289
JNZ
TRMIN
JNO*APPEND CRLF 4 UPDATE
0193
I NX
H
;.. .4 DEST PTRS
0290
JMP
LNDN 1
JYES*BACK UP
0194
JMP
MVRM1
; CONTINUE MOVE
0291
TPMIN: INX
H
JPOINT TO TAB
0195
MRDONj
MV I
M* CR
;CP/M END OF. ..
0292
TPMN0 : MVI
M* CR
JAPPEND CP/M...
0196
INX
H
;BUMP DEST PTR
0293
INX
H
J . . .LINE. ..
0197
MV I
M*LF
J . . .LINE MARKERS
0294
MVI
M*LF
J . . .TERMINATOR
0198
INX
H
;bump for next avail dest
029 5
INX
H
JUPDATE DEST PTP
0199
SHLD
DEST
JUPDATE POINTER VARIABLE
0296
SHLD
DEST
JUPDATE DEST VARIABLE
0200
RET
0297
XRA
A
J SET Z FLAG FOR "NO OPERAND" RET
020 1
*
0298
RET
0202
GTNXT :
LHLD
LI NAD
;GET PTR TO LAST FORMAL LINE
0299
*
0203
MV I
D*0
; CLEAR HIGH OFFSET ADDR
0300
MOVOP : LHLD
SOUPC
J HL = NEXT SOUPCE PTR
0204
LDA
CCBYT
;get low ordep offset
0301
XCHG
J DE = SOUPCE PTR
0205
MOV
E« A
JINSTALL PAGE ADDR
0302
LHLD
DEST
J HL = FILE DEST PTR
0206
DAD
D
J MAKE NEW FORMAL LINE ADDR
0303
MV0P1 : LDAX
D
J GET SOURCE CHAR
0207
MOV
A*M
;GET FIRST CHAR OF NEW LINE
0304
CPI
CF.
JPPEMATUPE EOL?
0208
CPI
EOF
;IS IT ALS-8 END OF FILE
0305
JZ
LNDON
J NO OPEFAND FIELD FOUND
0209
RZ
jyes* ret with z flag set
0306
CPI
' *
JFI ELD DELIMITER?
0210
SHLD
LINAD
; UPDATE FORMAL LINE PTR
0307
JNZ
MV0P2
J WE HAVE AN OFEPAND
021 1
STA
CCBYT
;SAVE CHAR COUNT BY”E
0308
INX
D
JELSE CONTINUE...
0212
RET
0309
JMP
MV0P1
J... SEARCH FOP. OPERAND
0213
*
0310
MV0P2 : CPI
• . *
JALS-8 DUMMY OPERAND?
0214
MVLAB:
XCHG
.
;de = SOURCE PTP
031 1
JNZ
TRUOP
JNO* GENUINE OPERAND
0215
LHLD
DEST
;HL = NEXT AVAIL DEST PTR
0312
INX
D
JPOINT AFTER DUMMY OPERAND
0216
MVLB 1:
LDAX
D
;get source chap.
0313
JMP
MVDON
JUPDATE 4 RET
0217
CPI
• »
;ALS-8 END OF LABEL''
0314
TRUOP: PUSH
PSV
J SAVE THE CHAP
0218
JZ
MLDON
0315
LDA
ASCSV
J GET ASCII STRING FLAG
02 19
CPI
* * '
; INTEL END OF LABEL''
03 16
CPI
- 1
JFFH IF ASCI I STRING
0220
JZ
MLDON
0317
JZ
ASTMV
J YES* DELIMIT 4 MOVE STRING
0221
MOV
M* A
JMOVE THE CHAR
0318
POP
PSV
JRETRIEVE THE CHAP
0222
INX
D
J BUMP SOURCE...
0319
TRUP1 : MOV
M* A
JELSE MOVE CHAR TO DEST
0223
INX
H
J .. .DEST PTRS
0320
INX
D
J BUMP SOURCE PTR
0224
JMP
MVLB 1
JCONTINUE MOVE
0321
LDAX
D
J GET SOURCE CHAP
0225
MLDON !
MV I
M* * : •
J FORCE INTEL DELIMITER
0322
CFI
CR
JLINE DELIMITER?
0226
INX
H
J BUMP DEST PTP
0323
JNZ
TP.UP2
JNO EOL* POSSIBLE FIELD DELIMITER
0227
SHLD
DEST
JUPDATE DESTINATION PTR
0324
INX
H
J BUMP DEST PTR
0228
INX
D
J DE = PTR TO SOUPCE AFTER LABEL
0325
SHLD
DEST
JUPDATE DEST VARIABLE
0229
XCHG
.
J HL = SOURCE PTR
0326
JMP
LNDON
0230
SHLD
SOURC
0327
TRUP2: CPI
• '
J FIELD DELIMITER?
0231
RET
0328
JZ
OPDON
J YES* MOVE IS FINISHED
0232
*
0329
INX
H
JNO*BUMP DEST PTR
0233
MKTAB:
LHLD
DEST
J HL = DEST FILE PTP
0330
JMP
TRUP1
JMOVE NEXT CHAP
0234
MVI
M* TAB
JFORCE CP/M FORMATTER
0331
ASTMV: POP
PSV
JRETRIEVE SAVED CHAR
0235
INX
H
J BUMP FOR NEXT DEST PTR
0332
MOV
B* A
J SAVE STPING DELIMITER
0236
SHLD
DEST
JUPDATE VARIABLE
0333
CALL
CFDEL
JDELIMITER HOUSEKEEPING
0237
RET
0334
ASMV1: LDAX
D
J GET STRING CHAR
0238
*
0335
CFI
CR
JANOMALOUS RIGHT DELIMITER?
0239
M0V0C:
LHLD
SOURC
J HL = DEST FILE PTR
0336
JNZ
ASMV2
JNO* CHECK FOP NORMAL DELIMITER
0240
XCHG
J DE = SOURCE PTR
0337
CALL
CPDEL
JUPDATE TARGET FILE
024 1
LHLD
DEST
J HL = DEST PTR
0338
XRA
A
J MAKE A ZERO
0242
MV0C1 :
LDAX
D
J GET POSS OPCODE CHAR
0339
STA
ASCSV
JNO ASSUMPTIONS ABOUT NEXT LINE
0243
CPI
• *
JSPACE DELIMITER?
0340
JMP
TRMN0
JPREMATURE EOL = STRING DELIMITER
0244
JNZ
TSTAS
JNO* look for asc pseudo
034 1
ASMV2: CMP
B
JRIGHT STRING DELIMITER?
0245
INX
D
J BUMP SOURCE PTP
0342
JZ
ASDON
JSTRING IS MOVED
0246
JMP
MV0C1
J KEEP LOOKING FOR OPCODE
0343
MOV
M* A
JELSE MOVE CHAR DOWN
0247
TSTAS :
CPI
•A*
JPOSSIBLE ASC PSEUDO?
0344
INX
D
J BUMP SOURCE PTR
0248
JNZ
MVOCF
J NO* GO MOVE OPCODE r I ELD
0345
INX
H
J BUMP DEST PTP
0249
INX
D
JPT TO NEXT CHAR
0346
JMP
ASMV1
JCONTINUE STRING MOVE
0250
LDAX
D
J GET IT
0347
ASDON: XRA
A
J MAKE ZERO
0251
CPI
•s*
J TEST 2ND OPCODE CHAP
0348
STA
ASCSV
JCLEAR OPERAND SWITCH
0252
DCX
D
J BACK UP IN EITHER 3ASE
0349
CALL
CPDEL
J DO RIGHT DELIMITER
0253
JNZ
MVOCF
JFALSE ALARM
0350
LDAX
D
J GET CHAR AFTER OPERAND
0254
MVI
A* - 1
J MAKE DEFINITE NON-ZERO
0351
CPI
CR
JPREMATURE EOL?
0255
STA
ASCSV
JOPERAND WILL BE ASCII STRING
03 52
JNZ
ASDN1
J NOT YET
0256
XCHG
•
J HL > "A”* DE > DEST
0353
SHLD
DEST
JUPDATE DEST VARIABLE
0257
MVI
M* 'D*
J WE ARE MAKING...
0354
JMP
LNDON
J NOTHING AFTER STRING CONSTANT
02 58
INX
H
0355
ASDN1: SHLD
DEST
JUPDATE DEST VARIABLE
02 59
MVI
M* *B*
J . . .A PADDED "DB".•.
0356
JMP
MVDNl
JUPDATE 4 RET
Pag*! 32
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
27
0357
0PD0N:
I NX
H
;BUMP DEST PTR
0454
UCTST:
CPI
•A'
;LOVER LIMIT
0358
JMP
MVDON
;UPDATE 4 RET
.0455
JC
NOTUC
/•OUT OF BOUNDS
0359
*
0456
CPI
•Z’ + l
;UPPER LIMIT
0360
CPDEL:
MV I
M/GUOTE
/FORCE CP/M STRING DELIMITER
0457
JC
YESUC
;VI THIN RANGE
036 1
I NX
H
/‘BUMP DEST PTP
0458
NOTUC:
XRA
A
/•SET Z FOR INVALID RET
0362
I NX
D
;bump source ptr
0459
YESUC:
ORA
A
/* Z RESET ON VALID RET
0363
RET
0460
RET
.
0362i
*
046 1
*
0365
FNDCF s
LHLD
SOUP.C
;get source ptr
0462
TSAVE:
MV I
A/UNIT1 ;load unit/speed byte
0366
FDCF1:
MOV
A* M
;get source char
0463
STA
FNUMF
/‘UPDATE SOLOS VARIABLE
0367
CPI
CR
JEND OF LINE AFTER OPERAND?
0464
LXI
H/FNAME /’POINT TO CURRENT FILE NAME
0368
JZ
LNDON
/•COMMENT FIELD ABSENT
0465
LXI
D/THEAD J4 SOLOS HEADP BYTE
0369
CPI
* *
/•FIELD DELIMITER?
0466
MV I
B / 5
/•ONLY 5 ASCII CHARS ALLOWED
0370
JNZ
TSTCF
/•COMMENT FIELD FOUND/TEST FOR EMPTY
0467
MORE:
MOV
A/M
/•SHOVEL THEM INTO SOLOS HEADP
037!
I NX
H
/•BUMP SOURCE PTR
0468
STAX
D
0372
JMP
FDCF1
/•CONTINUE SEARCH FOR COMMENT
0469
DCR
B
0373
TSTCF:
CPI
•; *
/•COMMENT DELIMITER?
0470
JZ
SAVFL
/•EXECUTE THE SAVE
0374
JZ
TSCFl
/•VE MAY HAVE A COMMENT
0471
I NX
H
/•ELSE HACK AVAY
0375
CPI
• * •
/'THE OTHER WAY TO DELIMIT A COMMENT?
0472
I NX
D
0376
JNZ
OKCOM
JVE DEFINITELY HAVE A COMMENT
0473
JMP
MORE
0377
TSCF1*
I NX
H
/•POINT TO CHAR AFTEP SEMICOLON
0474
*
0378
MOV
A* M
/‘LOAD IT
0475
SAVFL:
CAL-
SPRAM
/•DO SOME HOUSEKEEPING
03 79
CPI
CP.
/COMMENT FIELD EMPTY?
0476
LDA
FNUMF
/•GET UNIT 4 SPEED BYTE
0380
JZ
LNDON
/•YES
0477
LXI
H/THEAD /-POINT TO SOLOS HEADP
0381
*
0478
CAL-
VTAPE
/•DUMP 256 BYTE BLOCK(S) TO TAPE
0382
0KC0M:
SHLD
SOURC
/•UPDATE SOURCE PTR VARIABLE
0479
RET
.
/•END OF TRANSMISSION
0383
LHLD
DEST
JHL = DEST PTP
0480
*
0384
MV I
m, *; •
/•FORCE CP/M COMMENT DELIMITER
0481
SPRAM:
LHLD
BOFP
/•ALS-8 > SOLOS HEADER
0385
I NX
H
/‘BUMP DESTINATION PTP
0482
SHLD
LOADR
0386
SHLD
DEST
/‘UPDATE DEST PTR VARIABLE
0483
PUSH
H
;SAVE FOR THE MOMENT
0387
JMP
OKRET
/•SET FLAG FOR "COMMENT PRESENT"
0484
LHLD
EOFP
JEND > HL
0388
*
0485
XTHL
.
JSVAP TOP OF STACK
0389
MOVCF:
LHLD
SOURC
/•GET SOURCE FILE PTR
0486
MOV
A/L
/•COMPUTE BLOCK SIZE
0390
XCHG
.
/•DE = SOURCE FILE PTR
0487
CMA
0391
LHLD
DEST
z*HL = DEST FILE PTR
0488
MOV
L/A
0392
JMP
MVRM1
/•MOVE COMMENT FIELD DOWN
0489
MOV
A/H
0393
♦
0490
CMA
0394
NDFIL:
LHLD
DEST
/•HL = DEST PTP
0491
MOV
H/A
0395
NDFL11
MV I
M/CTRLZ
/•FORCE CP/M END OF FILE MARK
0492
I NX
H
0396
MOV
A/L
;get ls addr byte
0493
POP
D
JGET START
0397
CPI
0FFH
;IS BLOCK FULL?
0494
DAD
D
JADD OFFSET
0398
JZ
NDFL2
JBLOCK FILL COMPLETE
0495
I NX
H
JINCLUDE EOF
0399
I NX
H
/•ELSE BUMP POINTER
0496
SHLD
BLOCK
JSHOVEL IT INTO HEADER
0400
JMP
NDFL1
/•LOOP A FILL WITH CP/M ENDFILE MARKS
049 7
RET
040 1
NDFL2:
SHLD
EOFP
/•UPDATE FOR DISPLAY A TAPE SAVE
0498
*
0402
RET
•
0499
* CRT
MESSAGE
HANDLER
0403
*
0500
*
0404
SPFIX*
LHLD
BOFP
;HL » START OF TARGET FILE
050 1
VDPP.T:
MOV
A/M
JGET CHAR FROM BUFFER
0405
SPFX0X
MOV
A/M
/‘FETCH A CHAR
0502
CPI
ETX
JIZZIT THE END?
0406
CPI
CTRLZ
JCP/M ENDFILE ENCOUNTERED?
0503
RZ
.
JSURE ENOUGH
0407
RZ
•
/•PASS COMPLETE
0504
MOV
B/A
JMAIS NON/SET IT UP!
0408
CPI
FILL
MS IT A DUMMY CHAR?
0505
CALL
VDM
J 4 VIDEO IT
0409
JNZ
SPMOR
/‘NO/ KEEP MOVING
0506
I NX
H
J 4 ADJUDICATE THE INDEX
04 10
MV I
M/ • *
/•SUBSTITUTE BLANK FOR DUMMY
0507
JMP
VDPRT
J 4 OBTAIN ANOTHER
041 1
SPMOR:
I NX
H
/•BUMP FILE PTR
0508
*
0412
JMP
SPFX0
/•LOOP A SEARCH
0509
* CONSOLE MESSAGE AREA
0413
*
0510
*
04 1 4
LCASE:
LHLD
BOFP
;HL * STAPT OF FILE
051 1
MSSG1:
DB
CR
0415
LCAS1:
MOV
A/M
;get A CHAR
0512
ASC
#F ILE
EMPTY#
04 16
CPI
CTRLZ
;ARE VE DONE?
0513
DB
CR
0417
RZ
.
/•YES
0514
DB
ETX
04 18
CPI
*; *
MS IT A REMARK LINE?
0515
*
0419
JZ
NEVLN
;yes/ ignore a look for next
0516
MSSG2:
DB
CR
0420
CALL
GETCF
/•ELSE LOOK FOR A COMMENT FIELD
0517
ASC
#TYPE:
: "A" FOR ASSEMBLY LANGUAGE FILE#
0421
JZ
LCAS1
/•NONE FOUND
0518
DB
CP.
0422
LOWER:
MOV
A/M
;get a comment char
0519
ASC
#
"T" FOR TEXT FILE#
0423
CPI
LF
/•ARE VE DONE YET?
0520
DB
CR
0424
JNZ
L0VR1
/•NO/CONTINUE CONVERSION
0521
ASC
#
ESC TO RETURN TO SYSTEM#
0425
I NX
H
/*HL = POSS NEV LINE
0522
DB
CR
0426
JMP
LCAS1
0523
DB
ETX
0427
L0WR1:
CALL
UCTST
/•TEST FOR UPPEP CASE
0524
*
0428
JZ
NXTUC
/•NOT UC/TEST NEXT CHAR
0525
MSSG3:
ASC
#SAVING CP/M FILE:#
0429
ADI
20H
/•ELSE BIAS UP
0526
DB
ETX
0430
MOV
M/A
/•REINSTALL IN FILE
0527
*
0431
NXTUC:
I NX
H
JBUMP FILE PTR
0528
MSSG4:
DB
CR
0432
JMP
LOVER
/•LOOP TO NEXT CHAR
0529
DB
CR
0433
*
0530
ASC
#VEPIFY? < Y/N)#
0434
NEVLN:
I NX
H
JPT TO NEXT CHAR
0531
DB
CR
0435
MOV
A/M
/•GET IT
0532
DB
CR
0436
CPI
LF
/•HAVE VE FOUND EOL?
0533
DB
ETX
0437
JNZ
NEVLN
/•NO/ LOOP A SEARCH
0534
*
0438
I NX
H
/•POINT TO START OF NEV LINE
0535
* PROGRAM GLOBAL APEA
0439
JMP
LCAS1
/•GO PROCESS IT
0536
*
0440
*
0537
ASCSV:
DB
0
/•ASCII STRING SWITCH
0441
GETCF:
I NX
H
/•POINT TO NEXT CHAR
0538
CCBYT:
DS
I
/‘CHARACTER COUNT BYTE
0442
MOV
A/M
/•GET IT
0539
DEST:
DS
2
J DEST FILE PTR VARIABLE
0443
CPI
LF
;eol reached?
0540
LINAD:
DS
2
JCURRENT FORMAL LINE PTP
0444
JZ
CFABS
/•COMMENT FIELD ABSENT/ SET FLAG
0541
SOURC:
DS
2
/•SOURCE FILE PTR VAPIABLE
0445
CPI
'; *
/•START OF COMMENT FIELD
0542
SYSSP:
DS
2
JSTORE CALLING SP HERE
0446
JNZ
GETCF
/‘NOT YET/ KEEP LOOKING
0543
DS
24
/•THIS IS THE STACK
0447
I NX
H
/•POINT TO FI PST CHAR IN COMMENT FIELD
0544
STACK:
ECU
S
0448
ORA
A
/•CLEAR ZERO FLAG FOP COMMENT PRESENT
0545
*
0449
RET
.
0546
END
0450
CFABS:
I NX
H
/•POINT TO POSSIBLE NEV LINE
0547
*
0451
XRA
A
JSET ZERO FLAG FOP. FIELD NOT FOUND
0452
RET
.
0453 *
Number 41
28
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Pago 33
E
3
P/m ©mid)
Pogrom C©mPQDbiiiity
BY JIM WARNER
Chemistry Board of Studies
Natural Sciences II
University of California
Santa Cruz, CA 95064 t^=^= -— ===== , 1 -aa
Disk operating systems—CP/M by Digital Research (D.R.)
for 8080’s and CDOS by Cromemco for Z80’s -have occasion¬
ally been called “virtually identical” (DDJ # 35). Cromemco’s
Users Bulletin (Dec. 1978) makes more specific claims:
.. CDOS was designed to be upwards CP/M-compat-
ible... This means that most programs written for
CP/M (versions upto [sic] and including 1.33) will run
without modification under CDOS. This also means that
programs written for CDOS will not generally run under
CP/M.”
Cromemco’s CDOS and CP/M share identical disk directory
structures. In both operating systems, machin e language pro¬
grams are loaded and commence execution at 100H. The pro¬
grams, termed ‘transients,’ make calls upon the operating
system for I/O operations through a single entry point (05H)
which is independent of the amount of memory in the host
computer. A JMP at the entry address passes control to the
operating system, resident in high memory.
Both CP/M and CDOS decode I/O requests from transient
programs according to a function number passed in the C-
register. CP/M provides codes 1 to 27 for access to disk files,
the console, printer and other I/O devices. CDOS, patterned
after CP/M, has adopted all of CP/M’s function codes. The
principal difference between the operating systems is that
Cromemco has included 14 additional codes not possessed
by CP/M. CP/M is not protected against out of range func¬
tion calls and the certain result of an illegal call is a crash.
Another difference is that function codes which open (15)
and close (16) disk files and search the disk directory (17,18)
return with registers pointing to the file name differently
arranged if the operation was successful. More important,
however, is that the returned value for an unsuccessful opera¬
tion is the same for CDOS and CP/M. The difference is
important only for programs which read the directory as data
(e.g., to prepare an alphabetized directory listing).
CP/M 1.4 contains three undocumented function codes
included in neither CDOS nor earlier CP/M versions. Two of
these are used to set (28) and monitor (29) read -only status
of disk drives. The nature of the last (30) is unknown to me.
The codes are used by some of the utility pro-ams distributed
by D.R. as part of the CP/M package.
Finally, CP/M’s “jump vector” table can be used in
programs that need direct access to I/O drivers. Such programs
Page 34
include track-at-a-time disk copiers, direct disk editors, and
utilities such as PASTOCPM (DDJ, page 12, No. 37) which
read files from non-CP/M structured diskettes. This table is
the interface between CP/M’s system independent portion
(BDOS) supplied by D.R. and the I/O routines (BIOS) supplied
by the system configurer. The description of the table and
the responsibilities of the I/O routines can be found in D.R.’s
CP/M System Alteration Guide.
The address of the jump vector table depends on the
amount of memory allocated to CP/M and unfortunately D.R.
has not specified how transient programs should locate it. As a
result many programs from the CP/M Users Group which
worked under CP/M 1.3 require modification to function with
CP/M 1.4. It is a safe bet that these programs are not CDOS
compatible.
From the CP/M perspective it seems an unmanageable task
to sort through 14 function numbers and treat them all as
exceptions to the normal operating system. Some of these
codes provide intricate (and dangerous) direct disk access.
Others provide features unrelated to I/O such as integer multi¬
ply and divide routines. Happily, many excellent programs for
Z80’s distributed by Cromemco are made serviceable with
CP/M on treating only 2 of the 14 additional CDOS function
codes.
The first is READ CONSOLE WITHOUT ECHO (128). The
result, a single character with the parity bit reset, is returned in
the accumulator. A complicating feature of CP/M makes it
necessary to bypass CP/M’s INTEROGATE CONSOLE
STATUS (11) function. This is required because this function
actually reads a character if one is available and saves it where
READ CONSOLE WITHOUT ECHO would be unable to find
it.
The second important function code is FORMAT STRING
TO FILE CONTROL BLOCK (134). HL points to the source
string, while DE indicates where the file control block is to
be set up. This procedure must pad the name and extension
in the file name with the proper number of spaces while
excising the period between them. The optional drive
designator at the head of the string must be decoded and
lower case letters must be converted to upper case.
One of the CP/M function codes must be given special
treatment. It is necessary to restore the accumulator after
a WRITE CONSOLE (2) function call. If this is not done
EDIT will not print control characters.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
29
An implementation of these modifications to the CP/M
run time environment is presented in FILTER. Programs we
have successfully run under our filtered CP/M include
Cromemco’s relocating macro assembler (ASMB 02.15), linker
(LINK), editor (EDIT 00.09), 8080 to Z-80 assembly language
mnemonic converter (TRANSLAT V.2.1), machine language
debugger (DEBUG 00.08) and 16K BASIC 5.0 (in 18.5K!).
The location and installation of the filter are the final
concern. The jump instruction at 05H will have to be changed
to route system function calls through the filter. The address
field of this jump instruction, however, serves a secondary
purpose. It is read by many transient programs to find the
highest memory location that they can use without running
into the operating system. This feature must be preserved.
Our solution is to put the filter in the memory page
immediately below CP/M’s BDOS with the entry jump instruc¬
tion suitably modified. Its installation is similar to CP/M’s
DDT in that FILTER, loaded initially in low memory, boosts
itself into operating position. FILTER is not a permanent
modification to CP/M. Rather, as explained in the listing, it
is made a part of the memory image of the Cromemco
programs which require it. The location of the installed filter
will depend on the amount of memory available to CP/M. To
accommodate variable memory sizes, FILTER contains an
installation section which configures the actual filter to run
at the top of the transient program area.
To implement FILTER you will need to provide a system
dependent value for the equate IGOR. This determines where
FILTER will jump if it encounters an untreated CDOS func¬
tion code. If you have a ROM monitor program that preserves
the registers, put its entry address here. Lacking same, setting
IGOR to zero will force CP/M to reboot. This will destroy
the evidence (C-register) of the offending function code,
however.
If your standard console input routine includes code which
backs up the cursor and erases characters when you type
rubout you will probably experience strange behavior in
BASIC and EDIT. The easiest cure is to include a simple key¬
board input routine within FILTER in place of ‘GBYTE: JP
Z,DUMMY’. If you make this modification be sure to remove
the four instructions in part I which modify the address field
of the JP instruction. These instructions are marked with
*’s in the comment field of the program listing. If you make
changes that lengthen part III by more than about 18 bytes
you will also need to change the instructions in part II that
set the stack pointer below BDOS. Finally, if your basic
input output system (BIOS) changes the Z-80 index registers,
you will run into difficulties that we have not fully
documented.
Filter does not resolve all differences between CDOS and
CP/M. One deficiency is that the DIR command in BASIC will
give meaningless (but harmless) results. The ability of BASIC
to work with disk files is not, however, in any way impaired.
It will usually be necessary to hit the ‘esc’ key twice instead of
once to stop a RUNning BASIC program. BASIC and DEBUG
contain commands to utilize the programmable timers and
BAUD rate selection hardware found on Cromemco I/O cards.
These commands will not work without Cromemco hardware.
The present Cromemco software license agreement restricts
the use of their software to a single computer of their
manufacture. FILTER therefore will be of use primarily to
owners of Cromemco computers who cannot run CDOS
because their disk controller was manufactured by another
company.
Number 41
30
The author is a physical chemist at the University of
California at Santa Cruz. He is shepherd to a small flock of
microcomputers used in several laboratories for data
acquisition and apparatus control in transient spectroscopy,
molecular dymmics, chemical kinetics and nonlinear
dynamics.
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Pago 35
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Pago 36
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
31
Changing SPI Formatted
Programs to CF^M
Compatible Text
BY MARKM. ZEIGER
198-01B 67th Ave.
Flushing, N.Y. 11365
Many computer hobbyists who started a few years ago with
relatively simple equipment probably used assemblers such as
Processor Tech’s SPI or ALS-8. Now they have ‘graduated’ to
more sophisticated operating systems, CP/M being the most
prevalent. Think of all those great source programs still on
your cassettes that you would love to rewrite to use with
CP/M. However, who has the time to do all that retyping?
Computer to the rescue! The following program will change
source programs written by the SPI executive (as well as pro¬
grams written by ALS-8, XEK, and the PDS assemblers to
name a few) to text acceptable to CP/M assemblers and
editors.
The program is quite simple to use. First the SPI file must
be saved on the CP/M disk. Load the source into RAM at
100H. Then boot in CP/M and type
SAVE xx NAME.EXT.
Next run the change program by typing the command line
CHANGE NAME1.EXT NAME2. EXT
the text so that labels, code, and comments are neatly placed
in columns. The end of the SPI file is denoted by an 01
which is searched for by MOVEREC. The subroutine RE-
STORENEG is called only if a line number is located in two
different records. Any run-time error will abort the program
with an appropriate message. The CP/M file will not be written
if there is an error.
where NAME1 is the name of the SPI source file and NAME2
will be the name of the CP/M compatible file. Each file may be
prefixed by a drive designation. For example, the command
A >CHANGE B:LIST.SP1 LIST.ASM
will change the file on drive B called LIST.SP1 to a CP/M
compatible file called LIST.ASM and will write the file on the
logged-in drive (A). Note that both the source and destination
file must be specified when running the program or a run-time
error will occur.
Much of the program is self-documented. Studying the
CP/M interfacing guide and the program will help in under¬
standing most of the program’s logic. The major subroutine is
MOVEREC. This routine reads in one record (128 bytes),
takes out the fine numbers and character count found in
SPI text, and substitutes a carriage return-line feed for the
single carriage return in the SPI source. It will also format
Number 41
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Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page' 37
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Page 38
Dr. Dobb’s Journal of Computer Calisthenics 81 Orthodontia, Box E, Menlo Park, CA 94025
Number 41
33
At******************************************************
CPM-Pen /
PcnCPM
BY ROD HALLEN
Road Runner Ranch
P.0. Box 73
Tombstone, AZ 85638
The following letter written by Rod Hallen to Jim Gagne
is a fitting introduction to the listings which follow.
Dear Dr. Gagne,
In March I wrote to thank you for your Electric Pencil to
CPM routine (DDJ #33). I have found this to be one of my
most used programs. Thanks Again.
Recently I acquired Digital Research’s “MAC” macro
assembler and was looking for a project to use it on. That’s
how I learn the ins and outs of any software that I add to
my library. I decided to see if I could simplify and speed
up your program. The enclosed PRN listings are the result.
The limited length of PEN-CPM and CPM-PEN are due to
the macro routines which handle all disk I/O. Have you tried
“MAC”? If not, it is well worth the price. Both of these pro¬
grams were written in less than 3 hours time; an easy after¬
noon’s work.
I wrote these as two separate programs since 95 per cent
of my conversions are from Pencil to CPM. I write my as¬
sembly listings on the Pencil, convert to CPM, and test. If
something isn’t right (most of the time!), I reload the PCL
file into Pencil and try again. I have also eliminated tab
handling in PEN-CPM and line length considerations in both.
I only use these programs for assembly language listings and
never use a line longer than 72 characters.
You mentioned in your DDJ article that you were attempt¬
ing to change the disk read and write to 512 byte blocks.
This is extremeley simple with “MAC.” Note the 1024 at the
end of the INFILE and OUTFILE lines in the programs.
This is the number of bytes read or written at one time. The
only limit on this is the amount of memory that you have
available for buffers. Almost everything that your program
acccomplishes is handled automatically by the routines in the
SEQIO (SEQuential I/O) libarary which comes with “MAC.”
I’ve added one routine to SEQIO. LIB. That is MESS
which is my message printer. It is described in PEN-CPM.DOC.
These two programs have accomplished many things for
me. They have cut down on disk activity, reduced the con¬
version time, and eliminated a bug I couldn’t get out of
PENCPM. They have also made me aware of the capabilities
of macro assembling.
The bug usually left garbage at the end of an assembly
language listing that had been converted from Pencil to CPM.
This garbage consisted of the last few lines of the listing re¬
peated one or more times. This didn’t, however, affect assem¬
bly because my assemblers stop at the first END OP code.
As proof of the increase in conversion speed, PEN-CPM
takes exactly half as much time as PENCPM. The same is
true in the opposite direction. I have one question about
PENCPM. You save the old stack pointer and set up a new SP,
which I think is a good idea for any program that will use the
stack extensively, and then restore the old stack at the end.
However, then you call for a CP/M warm start which restores
the old stack pointer again. Why not a simple RET at the end?
This returns to CP/M without disk activity and is quicker.
I am sending a copy of this letter and the enclosed pro¬
grams to DDJ for possible publication. I am also sending a
disk copy of both source and command files to the CP/M
Users’ Group for inclusion in one of their library disks. If
you do not have “MAC” and you would like a copy of the
command files, please send me a soft-sectored 8” diskette
and $5 and I will record them for you. I find it necesssary
to charge for this service since programming and writing are
my only income.
Sincerely,
Rod Hallen
Number 41
34
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 39
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Number 41
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Number 41
36
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 41
PASTIMES
AND
PLEASURES
BY CHARLES WETHERELL
The Programmer’s Book of Rules
This month I would like to laud a singularly courageous
act by a friend of mine. George Ledin, Jr. and his brother
Victor have just published A Programmer ’s Book of Rules
(Lifelong Learning Publications, 1979. $7.95). Before I tell
you why I think George is so brave, let me describe the book.
Then we shall anoint the hero.
Handbook and Sourcebook
The most striking thing about Rules is its layout. On the
left of each double page are large boxes with a programming
rule in big black type; for example:
Nest Loops Sparingly.
Often there will be short subsidiary rules and references
to the source of the rule. On the right hand page there is an
explanation box for each rule box. The explanation is usually
English text, but it may contain a short program example,
an input sample, or an output fragment. The explanations
provide the reasons for the rules.
The book is broken into three major sections—one each
for requirements analysis, coding style, anil programming.
The sections fall into chapters; with each chapter comes a
bibliography giving exact sources for each rule in the chapter.
At the end of the book there is a collected bibliography
divided into useful topics. There is also a complete index of
authors and an index of subject headings. Rules is valuable
for its bibliographies alone.
When you first hold a copy of Rules, you will probably
want to read it straight through—two hours will do nicely.
Then you may well want to argue the rules with your friends.
Finally you will probably want to write your own Book of
© 1979, Charles Wetherell
Page 42
Rules. In fact, I predict that many readers will rip the spine
off Rules, hole-punch the pages, put the resulting handbook
in a loose-leaf binder, and start adding rules of their own.
George and Victor surely would approve. Rules not only sug¬
gests keeping historical notebooks, but the authors promise
to revise Rules from time to time and ask their reader’s help.
So keep those cards and letters coming, folks.
Where Angels Fear To Tread
What makes the Ledins so heroic? On the day I received
my copy of Rules, an acquaintance dropped into my office.
He picked up the book, riffled the pages, glanced at a few
rules, tossed it down, and said, “That can’t be right; at least
75% of the rales are all wet.” I fear that Rules is going to re¬
ceive the same reaction from many old-timers (perhaps
even from some of the quoted rule-makers). But such quick
criticism is beside the point; let me explain why.
First, every programmer needs discipline—discipline in the
monkish sense of a rule of fife. (By the way, George Ledin is a
professor at University of San Francisco, an eminent Catholic
school. Make of that what you will.) Almost any rule is better
than no rale at all. In fact, my master rule (or meta-rule,
if you will) is
If you did something before and you have to
do it again, Do It The Same Way.
In other words, make rules and stick to them.
Second, George and Victor didn’t make the rules up them¬
selves. They distilled the experience of many other expert pro¬
grammers. If you don’t believe the explanation for a rule, they
point you right to the original source, chapter and verse. You
can go read the rulemaker’s arguments and decide for yourself.
One of the most important rules is “Learn From Experience,
Yours And Others’ ”. Rules helps you do that.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia. Box E, Menlo Park. CA 94025
Number 41
37
Third, no rule is an absolute — neither “ Brush after every
meal” nor “Thou shalt not steal.” Programming rules are very
susceptible to exception. Criticism like the example at the
beginning of this section is very likely based on experience of
exceptions, but that doesn’t mean the rules are all wrong.
Judgment in application is needed. For example, I agree
wholeheartedly with the book’s rule “Avoid FORTRAN arith¬
metic IF,” but. .. when I write a binary search, it is the
perfect control structure. When you acquire the judgment
and experience, you too can break the rules.
So I fear the Ledin’s will receive much criticism and cen¬
sure. But they have done a service and they must be praised. I
have had a file of similar rules for five years and I have been
afraid to print. Not they.
Hair Splitting And Head Shrinking
So that George’s head doesn’t swell too big from all this
praise, I am now going to engage in a bit of criticism. Of
course, the Preface says comments are welcomed. So George
will now be noble for several paragraphs and take his licks
without flinching.
Rules contains a lot of material on control structures. Yet I
missed an overriding rule — one that says clean control has
clean mathematical structure. Similarly, in the section on de¬
bugging and testing there is no mention that the goal is to
write programs that are so clear and obvious that it is evident
on their face they contain no errors. In a very important sense,
debugging and testing are a waste of time; if your program
were correct from the start, you wouldn’t need to kill bugs.
While I think the mathematical theory of programming is no¬
where near developed enough to cope with large practical
programs, programmers must always keep the ideal of the
perfect program in mind. Rules does not emphasize this ideal
enough.
There are a few rules I believe must have slipped by when
George wasn’t looking. “Minimize compilation time” is one
such. Whatever for? Even very small computers have quite fast
compilers nowadays, and anyway, who cares how long the
compiler takes? Run-time, Si! Compile-time, No!
On the same quibble level. Rules suggests first that
comments should explain the why and wherefore of each
logical section of coding and that the code itself should
express the actions necessary to achieve the object. Then Rules
says one line of comment to 10 or 20 lines of code. I should
have thought one to one was a much better ratio. Surely 5%
comments are far too few. By the way, I do agree that a para¬
graph of comments should precede a paragraph of code; the
two should generally not be mixed.
Throughout Rules, the Ledin’s urge that clarity not be
sacrificed to efficiency. They also recognize that sometimes
improved efficiency is necessary. But nowhere can I find a
mention of the way efficiency is best gained — wholesale
replacement of algorithms and data structures by better ones.
I am reminded of a friend who spent much effort delicately
hand-coding an assembly language sort routine to extract
every last microsecond of speed. No doubt he developed the
fastest possible sort - using his algorithm. But along came a
graduate student who coded a well-known better algorithm in
ordinary FORTRAN. A factor of 3 speed-up and the new
algorithm only used 40% of the data space. Finally, the new
algorithm was simpler and cleaner. It often works that way.
Speed and elegance go hand in hand because both depend on
deep insight into the problem to be solved. So do follow
Rules’ precept to read the literature when you want more
efficiency.
Hobbyists and Rules
In spite of the criticisms, I still think that Dr. Dobb’s
readers will find Rules profitable. My guess is that most of you
are hobbyists and, even if involved with computers profession¬
ally, are not trained programmers. So you are probably having
to leam all the painful lessons of programming for yourselves.
Rules condenses much experience into palatable droplets of
wisdom; it would be foolish to turn down such a healthy
draught. Perhaps not all the ingredients will help you grow
into better programmers, but like Mama’s chicken soup, can it
hurt?
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Munlo Park, CA 94025
Number 41
38
Pa09 43
CARRY FLAG STILL W AVES
Dear Suzanne:
We wouldn’t want you not to have an 8080 pusher-popper
routine to kick around anymore, so I would like to make this
comment on the code submitted by John Bockelmann in DDJ
#38. May I be the umpteenth programmer to point out it
will always return with the carry flag cleared!! The DAD
instruction used to get the old SP modifies the carry flag,
and when DADing to 00, it will clear it. I don’t have an op¬
timum solution, but here is an idea of how we handle the
problem in our Fast! tm software:
SHLD HLREG
PUSH PSW
LXI H,2
DAD SP
SHLD OLDSP
POP PSW
LXI SP, NEWSP
;save HL in RAM
?ave CARRY flag
;this uses 1 level of the old stack
,the 2 makes up for the PSCH PSW
•JHL = true stack
;store old pointer in RAM
get it back
?et new stack
Now the registers can be pushed in any order. 'Vhat to do after
that depends on whether this is a subroutine, part of inline
code or whatever. Obviously, the code is not reentrant, re¬
quires RAM and is cumbersome. I am offering it as a stimulus
to your readers to find a better way and to keep the ol’
pusher-popper controversy going.
Sincerely, Brown Dog Engineering
Orv Balcom Box 427
Lomita, CA 90717
CP/M MACRO ASSEM
2.0
*001
SAUE A
RESTORE MACHINE STATUS
TITLE
'SAUE A
RESTORE MACHINE STATUS'
THIS
ROUTINE
WILL SAUE ALL REGISTERS IN THE 8080 AND INITIALIZE
THE STACK POINTER TO
A LOCAL STACK.
0000
E3
>AUE:
XTHL
JSAUE HAL
0001
D5
PUSH
D
;SAUE DAE
0002
C3
PUSH
B
JSAUE BAC
0003
F5
PUSH
PSW
JSAUE ACCUMULATOR A FLAGS
0004
EB
XCHG
JPUT RETURN ADDRESS IN DAE
0005
210O00
LXI
H, 0
JGET AND SAUE THE CONTENTS OF THE STACK POINTER
0008
39
DAD
SP
0009
222000
SHLD
SPH0LD
000C
314200
LXI
SP•LCLSTK {INITIALIZE THE LOCAL STACK
000F
EB
XCHG
0010
E9
PCHL
JPUT RETURN ADDRESS IN HAL AND GO THERE
THIS
ROUTINE
RESTORES THE MACHINE STATE USING THE SAUED
STACK POINTER ADDRESS "SPH0LD", AND THEN RETURNS TO THE CALLING
PROGRAM.
0011
2A2000
?ESTR:
LHLD
SPH0LD
JPUT SAUED STACK POINTER ADDRESS IN HAL
0014
F9
SPHL
{TRANSFER IT TO THE STACK POINTER
0013
FI
POP
PSW
{RESTORE ACCUMULATOR A FLAGS
0016 Cl
POP
B
{RESTORE BAC
0017
D1
POP
D
JRESTORE DAE
0013
El
POP
H
{RESTORE HAL
0019
C9
RET
{RETURN TO THE MAIN PROGRAM
THE FOLLOWING SUBROUTINE DEMONSTRATES THE USAGE OF THE TWO
SUBROUTINES SHOWN ABODE. THE MAIN PROGRAM CALLS THE ROUTINE CALLED
"LCLSUB". "LCLSUB" THEN CALLS "SAUE" TO PRESERUE THE MACHINE STATE
AT THE TIME THAT IT IS CALLED. WHEN ••LCLSUB” HAS COMPLETED
PROCESSING, IT THEN JUMPS TO "RESTR" TO RESTORE THE MACHINE
STATE AND RETURN TO THE CALLING PROGRAM.
AN’/ LOCAL ROUTINE
001A
CD0000
LCLSUB:
CALL
SAUE
JSAUE THE MACHINE STATE
{PERFORM ANY PROCESSING REQUIRED AT THIS
{POINT.
001D
C31100
JMP
RESTR
{LOCAL PROCESSING COMPLETE - RETURN TO CALLING
{PROGRAM WITH THE MACHINE STATE RESTORED
MAIN
SYSTEM STACK HOLD AREA A LOCAL STACK
0020
0000
SPHOLD:
DW
0
{MAIN PROGRAM STACK ADDRESS HOLD AREA
0022
DS
32
{RESERUE 32 BYTES OF STACK
0042
a
LCLSTK
EQU
*
{AND TAG THE TOP OF THE STACK
0042
END
JULIAN DATE
QUARREL WITH DAD
Dear DDJ:
1 take exception to the routines submitted by M. John
Bockelmann (DDJ #38) in the the “DAD SP” instruction
found in the save routine will modify the setting of the carry
flag before it is saved. Enclosed is a modified version of the
routines that will cure the problem.
I enjoy your publication very much and consider it to be
the best software journal for microprocessor programmers
available today.
Sincerely, 3660 London Road
Chester P. Quinn Chamblee, Georgia 30341
Dr. Dobb’s:
The letter by Jack Dekok in DDJ #39 reminded me that
The Government, in its usual wisdom, has managed to con¬
fuse things. Julian date is a precisely defined astronomical
term. According to the Explanatory Supplement to the
American Ephemeris and Almanac, the Julian Day Number
is the number of days since Noon, January 1, 4713 B.C.
(Julian proleptic calendar). The Julian Date at any instant
is the Julian day number, followed by the decimal fraction
of the day elapsed since the preceding noon. Julian dates are
always referred to as Greenwich Mean Time or Universal
Time. Noon was chosen as the time a new date starts be¬
cause the Greenwich astronomers did not like to have then-
date change in the middle of their night-time observations.
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
39
As Mr. Dekok says, Julian dates are much more convenient
to use than conventional Gregorian calendar dates for the com¬
putation of intervals in days. This letter is being written at
about 8 pm EDT, 25 September 1979 or JD2444142.5. It is
easy to find that 1 January 1984 (JD2445700.5) will be
upon us in only 1558 days. Unlike the governmental version
(which is better called the Annual Day Number, or simply
the Day number) the true Julian date does not require remem¬
bering which years are leap years. There are several good
formulae for conversion of JD to calendar date and vice versa.
A useful reference is Matrix Magazine Issue #3 (published by
Michael and Margaret Erlewine, 1041 North Main Street,
Ann Arbor MI 48104). Astronomers will find JD especially
useful in generating positions of the Sun, Moon, and the
planets with series expansions from the Explanatory Supple¬
ment. Matrix has also published useful formulae for such
purposes.
I have no idea why the government created its own “Julian
date.” I suspect it was a case of someone who vaguely re¬
membered AST 1 Lab ... but not too well. If anyone knows
more about the origins of the error, I would appreciate hearing
from them .
Sincerely, Astronomical Time Mechanisms
John P. Oliver P.O. Box 12248, University Station
Gainesville, FL 32604
ADDITIONAL NORTHSTAR DOS PATCHES
Dear DDJ,
I would like to make some additions to Mr. A.M. Banks’
Northstar DOS patches (DDJ #39, page 43). The changes to
be made are as follows:
WAS: 2601 FE01
2603 C2 11 26
2611 CD 0C 27
29F3 C3 14 26
29F6 06 07
29F8 CD 04 27
CHANGE TO: 25DB FE02
25 DD CA EE 29
25EB CDF6 29
29F3 C3EE25
29F3 C3EE25
29F6 0E 07
Also to incorporate the ‘GOTO’ data change :
217AFE01 217A FEXX
217CC2 89 21 217C D2 89 21
The ‘XX’ can be any number since I use different type
numbers for electric pencil files, proc. tech, music files, and
other BASIC files such as tiny BASIC. The reason for ‘FE 02
CA EE 29’ is that type 2 files use byte number 13 for the
number of active blocks in a BASIC program. A BASIC state¬
ment such as l A = CALL(8229.1)’ will display the directory
from a BASIC program.
Thanks again for the magazine and keep up the good work.
Sincerely, PO Box 384
Jim Gammell Berwick PA 18603
STRING ARRAYS IN NORTHSTAR BASIC
Dear DDJ:
This letter is in reply to a remark made in passing in ore of
the book reviews in the September 1979 issue of Dr. Dobb’s
Journal. At the end of the first paragraph in the second review
on page 43, the remark was “Did you ever try to figure out
how to handle string arrays in Northstar BASIC?” Well, I have,
so I thought I would share these routines.
These examples are just to illustrate my approach; the
details will probably have to be changed in an individual
program, but they can be used as starting points. The idea is
to store all of the string entries consecutively in a single tong
string variable and use an associated numeric array for pointers
to the end of each string element.
The arrays ran be set up by routine #1. If the program
requires a string array with fixed data, the same loop can use
READ/DATA statements instead of the INPUT statement.
If the total number of entries is not known in advance, use a
loop controlled by IF/THEN statements to check for an
ending signal (sin input of END, QUIT or something similar).
The required string element can be accessed by using the
expression A$(N-1)+1 ,A(N)), with N being the number
of the entry. This works because A(N - 1) is the pointer to the
last character of the entry ahead of the required entry, so
A(N- 1) + 1 points to the first character and A(N) points to
the last character of the required entry. Note that for the first
entry, N=1 so A(N - 1) = A(0), this must be zero. Of course,
it is automatically set to zero when the array is dimensioned,
but it is a good idea to keep this requirement in mind anyway.
If this expression is required repeatedly (it probably
will be) it is simpler to use a defined function such as DEF
FNA$(N) = A$(A(N-1)+1 ,A(N)). This can be called
by expressions such as PRINT FNA$(N) or T$ = FNA$(N).
It is rather more difficult to dynamically alter the array
string, but the defined function, shown as routine #2, will do
it. This can be called by expressions such as X = FNA(T$,N),
where T$ is the new string to be inserted and N is the number
of the entry to be replaced. If the number of entries (N9 in
this example) is unknown or otherwise not readily available,
the pointer array can be set up with an extra entry at the
end which is set to zero or negative. Then the FOR/NEXT
loop and line 140 can be replaced with IF /THEN statements
to check for this end marker in the pointer array.
I want to emphasize that these examples are intended
strictly as starling points. Depending on the requirements
in your program, they may have to be extended greatly.
They do work in Northstar BASIC, but I don’t know how
much they need to be changed for other BASICs which may
also require a similar approach to simulate string arrays. Also,
I haven’t shown the obvious additional requirements, such as
properly dimensioning everything first.
Compared to a BASIC which directly handles string arrays,
these routines are somewhat inconvenient and inefficient, but
they do work. So now you can go ahead and copy those
programs that you haven’t copied before because they used
string arrays! Good luck, and have fun!
Number 41
40
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, M 3nlo Park, CA 94025
Page 45
A little further explanation may be helpful to those who
are not familiar with the way the string functions are used in
Northstar BASIC. First, dimensioning a string does not set up
an array of strings, but sets up a single string. The specified
dimension is the maximum length of this string. Substrings
are invoked by either 1 or 2 subscripts, as in A$(2,5) or
A$(4). The first example results in the second through the
fifth characters of A$, and the second example results in the
fourth through the last characters of A$. 11118 same format
cm be used in assignment statements also. For example,
assume A$ is ABCDEFG, the statement A$(3,5) = “123”
results in A$ now being AB123FG.
Sincerely, 2232 Alameda Avenue
Larry Hudson Ventura, CA 93003
Hudson adds the following information in a note: “Until I
got my Altair I had no experience or training with computers.
Even after I got it, everything I have learned has been from
books and my own playing around with it. BASIC is the only
high-level language I am familiar with, but I do most of my
programming in 8080 assembly language. I men wrote my own
assembler, also the editor I am using to write this letter. ”
ROUTINE 111
1(0 A(=""\REM - set the array string to a null string
110 FOR 1=1 TO N
120 INPUT Tl
130 A*-fl*+T*\A(I)=LEN(A*)
140 NEXT I
ROUTINE 112
100 DEF FNA(T*,N)
110 U=LEN(T$)+A(N-1)-A(N)\REM - ^difference btun old X new
120 IF N=1 THEN 130 ELSE 140XREH - special handling for 1st
130 A$=Tt+A((A(N)+1)\60T0 170
140 IF N=NV THEN 150 ELSE H0\REH - spcl handling for last
150 A»=A»(1,A(N-1))+T»\G0T0 170
140 A*=A * < 1 ,A(N-1 ))+T*+AKA(N)+1 INRErt - insert new string
170 FOR I=N TO N9XREN - N?=nunber of entries
180 A<I)=A(I)+D\REM - update pointer array
190 NEXT INRETURN 0
200 FNEND
A CORRECTION TO KRAY’S TABLE
Dear Suzanne:
Your letter dated September 10 re the error in the Machine
Language Program Displacement Table (DDJ #38) reached
me a few days ago via my home address in Australia and I
have just received a copy of the September issue of DDJ. In
fact a second error has crept into the same paragraph. But
they were not the fault of the Table. The Table gives correct
results every time if the directions are followed properly.
The two errors in the paragraph beginning “Besides calcu¬
lating program displacements...” baffle me. The article was
checked God knows how many times after successive drafts
were typed. But I must have slipped up in the final draft which
I mailed to you. I haven’t a copy of the typescript with me
in Canada but I seem to recall inserting the word “(hex)”
in the final version to make it clearer, which suggests the error
got into the penultimate version which followed a thorough
check of the hexadecimal arithmetic using a TI hex calculator
by a colleague who owns one. Anyway, that offending para¬
graph, for which I must shoulder the blame, should contain
37B9 in place of 27B9 and in the last line 9 rather than 19
(hex) bytes. Here is a corrected version of the offending para¬
graph:
Besides calculating program displacements the table is
useful for determining the length of program segments, sub¬
routines, etc. For example, can a program extending from
37B9 to 3C63 be relocated in a gap between 0FA2 and 1455?
Using the table we find that the program is 4AA bytes in
length and the gap is found to be of 4B3 bytes, so it will fit
with 4B3-4AA equals 9 (hex) bytes to spare.
Yours sincerely, Visiting Scientist,
Colin Keay, Planetary Sciences Section
Dr. Dabb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 41
41
Page 46
SAVE AN UNALTERED 8080
Editor:
Here is a routine that saves the state of an 8080, yet leaves
it unaltered. As I mentioned in my last letter, such a routine
might be useful in a debugger or break-point monitor where
the current machine state must be obtained in a non-de¬
structive manner.
Cheers, P.O. Box 1057
Jon Bokelman Menlo Park, CA 94025
0FG
ROM
Jany ROM or RAM address
SAVE:
SELL
SAFHL
Jsave HL reg
STA
SATA
Jsave contents of accumulator
LXI
H,8000H
Juse HL to reflect status of flag 1
JM
TSTZ
{test S flag bit. Jump If 1
M0F
H,L
JH=0 means S=0
TST2 :
JNZ
TSTP
Jtest Z flag bit. Jump If 0
MVI
L, 40H
JL*40H means Z*1
TSTP:
JP0
TSTC
Jtest P flag bit. Jump If 0
INX
H
JL*04H means P*1
INX
H
INX
H
J(INX alters no flags)
INX
H
TSTC :
JNC
TSTH
Jtest C flag bit. Jump If 0
INX
H
JL=01H means C*1
;at this point H and L
contain the 'testable' flag bits
J the N
and H
flag bits
are obtained by deductive logic
TSTH :
MFI
A,240
Jvalue to test N and H flag bits
DA A
Jexecute DAA and see what happens
ANI
82H
Jmask the significant result bits
RAL
Jjuggle to correct position
PAL
RAL
{accumulator
now contains N and H flag bits
ORA
L
Jadd C, Z and P flag bits
ORA
H
Jadd S flag bit
STA
SAFF
Jsave reconstructed flag register
Jail flags saved, now save other registers
LXI
H, 0
Jget all zeros-
DAD
SP
J to get SP register
LXI
SP,SAFI
1 J(assume Interrupts disabled)
POP
PSV
{restore PSW
PUSH
PSW
Jand resave to fix bits 5, 3 and 1
PUSH
B
Jsave BC register pair
PUSH
D
Jsave DE register pair
PUSH
H
Jsave SP register (from DAD above)
SPHL
Jrestore original SP contents
LHLD
SAFHL
Jrestore original HL contents
Jail regs saved, machine state unaltered
»continue In-
-line code
or return
0RG
RAM
Jany RAM address
SAfSP:
DS
2
Jsaved SP
SATDE:
DS
2
Jsaved DE
SAFBC:
DS
2
Jsaved BC
SAFF:
DS
1
Jsaved Flags
SAFA:
DS
1
Jsaved Accumulator
SAFHL
DS
2
Jsaved HL
BASIC AIN’T THAT SLOW
Dear Suzanne:
In the October issue of Dr. Dobb’s ( #39) on page 30 there
is an article by David Morganstein regarding using OSI BASIC
with a modem. The statement was that BASIC is too slow to
keep up with even 300 baud. This is not true. Declaring any
numbers used in the first few lines of the program will help
to speed things up somewhat. However rather than using
PEEK to check the status use WAIT. Example:
10 P = 64512:M = 127:R = 13
Putting this rou tine in the beginning of the program should
also help. There are several routines in OSI BASIC that by
doing one or two POKES allows you to write a string to
memory rather thiin the CRT. By combining these features,
BASIC can receive, store and print without missing any char¬
acters at greater than 300 baud. This is not to say that this
would be preferable to assembler, only that it is possible.
Yours truly,
L. Barker Chicago, Illinois
INSTALLING A “PHANTOM-DESELECT”
Dear Editor,
I recently found it necessary to install a “phantom-de-
select” on one of the excellent GODBOUT ECONORAM II
boards. The following circuit has worked well, with no pro¬
blems.
1. Cut trace from pin 6 of IC5.
2. Cement a 74L800 (on its back) to the board next to
IC11. (It fits nicely on the ECONORAM II logo).
3. Connect as follows:
Board now works with Tarbell floppy-disk controller.
Sincerely Newberry Microsystems
Steve Newberry 24225 Summerhill
Los Altos, CA 94022
800 REMEMBER TO INITIALIZE VARIABLES
810 Q$ = ” ”
900 WAITP,1
910 X = PEEK (P + 1) ANDM
920 IFX = RTHEN?: RETURN
930 IFF = 1 THEN?CHR$(X);
940 Q$ = Q$ + CHR$ (X)
950 GOTO900
Number 41
42
Dr. Dobb's Journal of Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 47
© David Dameron 1979
43
Dr. Dobb s louRNALof
COMPUTER
^Calisthenics Orthodontia
Running Light Without Overbyte
Number 42
February 1980
Volume 5, Issue 2
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
TI 9900: Fully Reentrant Formatter Operating Under TIPMX 5
Norman V. Walters
A Table Driven Assembler On CP/ M 18
Darrel J. Van Buer
Feature Enhancements for the ADM-3A 15
John Wakerly
A User Interface to Apple-II Renumbering 26
Dewitt S. Brown
Converting Binary to Decimal 32
Dennis Allison
USCD PASCAL Terminal Parameters 34
Ronald G. Parsons
A Microprocessor-Assisted Graphics System 38
Griffith Hamlin and Thomas Crockett
... and, as always, even more
«/////«//////
E>QQ1
TI 9900
/ill]
XTV
nr/iww
H
FULLY REENTRANT FORMATTER
OPERATING UNDER
TIPMX
BY NORMAN V. WALTERS
Software Engineer
R&D Department
Fairfield Industries, Inc.
Houston, TX 77042
Our company felt the need for a program that would allow
assembly language programs operating in a real-time environ¬
ment to display information to and request inputs from the
user. The end result has been a powerful tool that is used in a
large portion of our ongoing efforts. The code has been
debugged over a period of six months in actual usage by a
number of different users and should present no major
“gotchas” to the unwary user.
There are five externally referenced routines that FRMTR
calls during its execution. They are the following: B$RAM,
CIO$$, ENTSM, PANIC, and RIOS. Since these called routines
would vary from system to system, they are not given, but are
instead described for the user to write for his or her own
application.
BSRAM is the separator for stack and relative addressing.
CIO$$ is the character I/O routine. The character to be input
will be in the most significant byte of R7. The routine will
input a character to the most significant byte of R7. The
inputs and outputs are always ASCII. R7 should be the only
register to change and then only on input. ENTSM is the work¬
space and stack allocator. PANIC generates an error message
for the selected output device. The message does not depend
on the formatter for generation of the message since it is
showing an internal error of the formatter. If the user does not
wish to generate this routine, the formatter code may be
changed to
B @ERR9
and the user can designate ERR9 as an internal error. RIOS is
the cursor I/O routine.
The system used for editing and assembly of this program
was a TI 990/4 'vith dual floppies and 810 line printer. The
program was debugged on TI 9900/ 101’s with one or two
Micropolis mini-floppies, 833ASR with dual cassettes,
ADM-1A terminal and SCI line printer.
The code could probably be maximized in some areas, but
we wished to get an operating program in use without
incessant polishing. The following documentation is the full
documentation I wrote to accompany the program. I hope
that the combination of the documentation and the copious
comments in the listing will enable you to understand FRMTR
fully.
Number 42
46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 5
TIPMX FULLY REENTRANT FORMATTING ROUTINE
Tfiis routine processes and performs nine (9) different functions at
the present time. Eight (8) opcodes are used, 0 through 7. The 4
most significant bits (BO-3) are used to designate the opcodes thus
aLlowing room for further opcodes if needed. The 12 least signifi¬
cant bits (B4-15) are used for instructions in a particular opcode.
CURABS - Outputs a command to position the cursor at Row (line) Y
and Column X relative to cursor home (upper left-hand corner of CRT).
Cursor home is Row 0, Column 0. The subroutine uses the following
registers for the following values:
REGISTER
VALUE
R6 ROW (LINE)
R7 COLUMN
OPCODE FUNCTIO N
0 1. END FORMATTING ROUTINE IF 12 LSB-0
2. FILL N COLUMNS WITH SPECIFIED
CHARACTER.
1 PRINT (OUTPUT) INTEGER.
2 POSITION CURSOR ABSOLUTE (RELATIVE TO
HOME POSITION).
3 INPUT (READ) INTEGER.
4 POSITION CURSOR RELATIVE TO LAST
POSITION OF CURSOR.
5 INPUT/OUTPUT STRING.
6 1. REPEAT FOLLOWING FORMAT N TIMES.
2. END FORMAT REPEAT
7 LINE FEED CARRIAGE RETURN OR SPECIALFUNCTION
CURREL - Outputs a command to position the cursor to Row (line) Y
and Column X relative to the cursors present position. This
subroutine uses the cursor read command to determine the present
position of the cursor, therefore it can not be used with CRT's not
having this command capability. The ADM-3A does not have this
capability, the ADM-1 does. The subroutine uses the same registers
and their values as the CURABS subroutine.
FORMAT OF LUNS FOR CALLING SEQUENCE
LUNS is used to designate the input and output devices to be used
with the formatting routine. It will be consist of two bytes. The
first byte will be the input device, the second byte will be the
output device.
For ease of use, the formatting instructions have been effectively
microcoded, the user does not have to work with bits.
C ALLING SEQUENCE OF FRMTR
LI Rll,FRMTR
BLWP RIO
DATA OPLST,FMTLST,LUNS
JMP ERR
NUMERICAL BASE
The routine is initialized to base 10. The base is changed by N or D
fields (do not use both in the same formatting command) in format
1 or 3. That base will then be used until it is changed again.
NESTING OF FORMAT LOOPS
EXIT FROM FORMATTER WHEN ERROR IS DETECTED
Formatter will return control to the calling program with three data
items supplied to the calling routine. R0 will return the error
code which will designate the portion of the formatter that detected
the error (see following table), Rl will contain the OPLIST address,
and R2 will contain the FMTLST address.
R0 VALUE
ERROR AREA
1
2
3
4
5
6
7
8
9
10
INVALID OPCODE
REPEAT NESTING ERROR
INPUT CHARACTER SYNTAX ERROR
REPEAT VALUE MORE THAN MAXIMUM ALLOWED
OUTPUT CHARACTER SUBROUTINE
INPUT CHARACTER SUBROUTINE
CURSOR POSITION OUTPUT ROUTINE
CURSOR POSITION INPUT ROUTINE
RESERVED (NOT PRESENTLY USED)
ESCAPE SYMBOL DETECTED
Nests up to eight (8) deep (determined by MAX in equate section) are
permitted. Opcode six (6) is used to start and erd a loop. Each
loop MUST have a SEPARATE end repeat format, i.e. there must be as
many end repeat opcodes as there are begin repeat opcodes.
DE FINITIONS OF CALLED FORMATTER SUBROUTINES
INCHAR - Reads a single ASCII character into the left-hand (BO-7)
byte of R7.
OC HAR - Outputs a single ASCII character from the left-hand (BO-7)
Byte of R7.
BI SBAS - Converts binary numbers to digital ASCII strings in base 2,8,
17, or 16. Determines the sign of the number and stores a plus (+) or
minus (-) ASCII character at the start of the string. The subroutine
uses the following registers for the following values:
REGISTER
VALUE
R5 WIDTH OF OUTPUT (NUMBER OF DIGITS)
INCLUDING SIGN IF ANY
R6 ADDRESS OF BINARY NUMBER
R7 BASE (2,8,10,16)
NEEDED EQUATES FOR FORMATTER MICROCODE
The user will need to include in the calling routine the following
equates:
B
EQU
>20
CRLF
EQU
>7000
OPCODE 7
D
EQU
>40
ENDFRM
EQU
>0
ENDREP
EQU
>6000
F
EQU
>800
I
EQU
>20
INPUT
EQU
>3000
OPCODE 3
L
EQU
>80
MOVE
EQU
>4000
OPCODE 4
N
EQU
>80
P
EQU
>800
PRINT
EQU
>1000
OPCODE 1
R
EQU
>80
ROW
EQU
>780
REPEAT
EQU
>6000
OPCODE 6
S
EQU
>400
SET
EQU
>2000
OPCODE 2
STRING
EQU
>5000
OPCODE 5
T
EQU
>400
TAB
EQU
>0
OPCODE 0
Y
EQU
>100
Z
EQU
>800
The maximum width of a number is dictated by the base and the fact
that only one word (2 bytes) of binary are considered. If the number
is a signed number,the maximum width is reduced by one to allow for
the sign.
At the end of the subroutine, the registers will have the following
values:
EXAMPLE OF PROGRAM USING FORMATTER
Appendix A contains a test program that uses microcode to test
Opcode 0 (TAB), 1 (PRINT), 2 (SET), 3 (INPUT), 4 (MOVE), 5 (STRING),
6 (REPEAT), and 7 (CRLF).
PROVISION FOR GETTING OPLIST, FMTLST, AND LUN ADDRESSES FROM STACK
REGISTFR
VALUE
R5 WIDTH (SHOULD ALWAYS BE POSITIVE)
R6 ADDRESS OF START OF ASCII STRING
R7 STATUS 0=GOOD l=ERROR
If any of these pointers are to be gotten from the stack, the calling
sequence for the formatter as shown on page 1 would be modified by
adding +1 to the pointer that will be obtained from stack.
EXAMPLE: It is desired to obtain OPLST and LUNS from the stack and
FMTLST from DSEG.
BASBIN - Converts ASCII digital strings (base 2,8,10, or 16) with
or without signs (+ or -) into a binary word (2 byt:es) . The
subroutine uses the following registers for the following values:
REGISTER VALUE
LI Rll,FRMTR
BLWP R10
DATA OPLST+1,FMTLST,LUNS+1
JMP ERR
R5 WIDTH OF STRING INCLUDING SIGN
(+ or -) IF ANY
R6 ADDRESS OF START OF ASCII STRING
R7 CONVERSION BASE (2,8,10,16)
The subroutine rejects any width that would result in a binary
number too large to be contained in one word (2 bytes).
At the end of the subroutine, the registers have the following
values:
IF USER INPUTS TOO MANY DIGITS FOR ONE NUMBER
The formatter examines the length of the input number. If the
maximum allowed is exceeded, the first character that exceeds
the maximum is examined. If the character is an allowed terminator
(i.e., COMMA, CR, SLASH, COLON, or PERIOD), the formatter will take
a normal exit and process the next format. If the character is not
a terminator, the formatter will wait until an allowed terminator is
input. It will not accept any further numbers.
IF STRING LFNGTH EXCEEDS FORMAT MAXIMUM
REGISTER
VALUE
R5 WIDTH (LESS 1 IF A SIGN WAS IN STRING)
R6 ADDRESS OF BINARY WORD
R7 STATUS 0=GOOD l=ERROR
If the maximum is exceeded, the first character that exceeds the
maximum is examined. If the character is an allowed terminator
(i.e., CR, ESCAPE, or NULL), the formatter will take a normal exit
and process the next format. If the character is not a terminator,
the formatter will exit and remainder of string will be ignored.
Pacje 6
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
47
o
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Q
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Number 42
48
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 7
Page 8
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
49
Number 42
50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 9
IDENTIFICATION: OPCODE 4 SET CURSOR TO RELATIVE POSITION
Paine 10
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
51
The microcode for OPCODE
tn
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in
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Number 42
52
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page I11
EXAMPLE PROGRAM CALLING FORMATTER
Page 12
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
53
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Number 42
54
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 13
-ft ★
North Star Disk
*
STOIC
*
Our November-December issue was barely in the mail when
I was tracked down on the telephone by a fellow named Bob
Fleming. “I've got some bad news for you,’’ he said. “That
STOIC program you’ve just published looks exactly like the
original STOIC program written by Jon Sachs a couple of
years ago in a joint Harvard-MIT engineering group. ”
I obtained a copy of Sachs’ program and quickly ascer¬
tained that Fleming was right: it was almost word-for-word
the same program. I called John Sachs, now at Data General in
Massachusetts. He told me that he developed the program in
1978 at the Harvard-MIT Health Science and Technology
Division’s Biomedical Engineering Center. He said the program
was available for anyone to use as long as credit for it re¬
mained with the Center.
B. W. Lee, the author of the piece which appeared in DDJ,
said, by way of explanation, that the later installments would
have been quite different than the first. That may, or may not,
be true, but we still felt, in all fairness, that Mr. Lee should
have attributed credit to Harvard-MIT and not signed his name
to work which he did not create. The fact that Mr. Lee was
charging a fairly significant amount of money to distribute
STOIC on tape has just about killed our interest in publishing
anything in the future for which the reader will have to pay
m ore than copying and mailing costs.
We have withdrawn the future installments of Mr. Lee’s
STOIC article. Instead, we are including information here on
ordering STOIC on tape direct from the Biomedical Engineer¬
ing Center.
We apologize to any reader who has been inconvenienced
by this unfortunate situation.
Procedure for Obtaining Copies of STOIC
An industry-standard magnetic tape (9-track, 800 BPI)
containing the STOIC program listings along with written
descriptions will be supplied upon request. /Vn index of 8080
STOIC programs and the description of tliis magnetic tape
follow:
STOIC TAPE DIRECTORY
M
PROG
NUMBER DESCRIPTION
☆
0 STOIC BOOTSTRAP
1 STOIC KERNEL
2 BASIC STOIC DEFINITIONS -
3 FILE SYSTEM ^
4 TEXT EDITOR
5 FLOATING POINT PACKAGE (4 Vi PLACE ACCURACY)
6 MISCELLANEOUS DEFINITIONS
7 FAST FOURIER TRANSFORM (FLOATING POINT)
8 LINE DRAWER AND GRAPHICS PACKAGE (DEVICE DE¬
PENDENT)
9 INTERRUPT HANDLER (SYSTEM DEPENDENT)
10 FIXED POINT SIN.COS
11 RADIX EXCHANGE SORT
12 DOUBLE PRECISION ARITHMETIC PACKAGE
13 STOIC WRITE-UP PART 1
14 STOIC WRITE-UP PART 2
15 STOIC ASSEMBLER WRITE-UP
16 STOIC KERNEL WRITE-UP
17 STOIC FILE SYSTEM WRITE-UP
18 STOIC EDITOR WRITE-UP
19 STOIC FLOATING POINT PACKAGE WRITE-UP
20 STOIC INTERRUPT HANDLER WRITE-UP
21 STOIC BOOTSTRAP WRITE-UP
22 STOIC INTIAL LOAD INSTRUCTIONS
TAPE FORMAT
NO LABEL jj
9 TRACK, ODD PARITY, 800 BPI
FIXED SIZE BLOCKS: 2640 BYTES (DECIMAL)
EACH BLOCK IS 20 132 CHARACTER LINE IMAGES (ASCII)
LINES ARE BLANK FILLED WITH NO CARRIAGE RETURNS
TABS ARE NOT CONVERTED TO SPACES
LINES CONSISTING OF A FORM FEED FOLLOWED BY 131
BLANKS SEPARATE PAGES
INDIVIDUAL PROGRAMS ARE SEPARATED BY A LINE
CONTAINING THE STRING “***EOF***’\
ALL PROGRAMS ARE IN A SINGLE FILE
TWO COPIES OF THE FILE ARE INCLUDED ON THE TAPE.
SEPARATED BY HARDWARE EOF AND TERMINATED BY
TWO EOF’S.
PROCEDURE:
1) MAKE LISTINGS OF ALL PROGRAMS AND WRITE-UPS
2) READ ALL WRITE-UPS
3) FOLLOW THE DIRECTIONS IN THE INITIAL LOAD IN¬
STRUCTIONS TO MODIFY PROGRAMS FOR YOUR SYSTEM
THE TAPE CONSISTS OF APPROXIMATELY 9000 (DECIMAL)
LINES OF TEXT (PER FILE).
WRITE-UPS
STOIC.WU
STOIC 1
STOIC 2
ED.WU
BOOT.WU
PAPER
MODS
FP.WU
FS.WU
RCV.WU
LETTER 1
COMPARISON
KERNEL
PROM.WU
INTERRUPT .WU
CODE
SYSGEN.WU
DESCRIPTION OF HOW TO GET STOIC
RUNNING ON A NEW MACHINE
STOIC WRITE-UP PART 1
STOIC WRITE-UP PART 2
TEXT EDITOR WRITE-UP 44
BOOTSTRAP WRITE-UP
MANUSCRIPT OF STOIC PAPER
LIST OF ALL SOFTWARE REVISIONS
FLOATING POINT PACKAGE WRITE-UP
FILE SYSTEM WRITE-UP
RCV WRITE-UP
DISTRIBUTION LETTER
8080 SIGNED AND UNSIGNED COMPARISONS
KERNEL WRITE-UP
PROM BURNING PROGRAM WRITE-UP
INTERRUPT HANDLER WRITE-UP
ASSEMBLER WRITE-UP
INSTRUCTIONS FOR GENERATING A NEW
BOOTSTRAP FILE AND RUNNING THE
COMPRESSOR
Requests should include a brief description of the
anticipated use of the STOIC programming system and should
include a blank tape and self-addressed, stamped mailing
container for its return. Address requests to:
Stephen K. Bums, Technical Director
Biomedical Engineering Center
for Clinical Instrumentation
MIT; Room 20-A 119
Cambridge, Mass .02139
Page 14
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
55
F€ATUR€ €NHANC€M€NTS
for ADM'OA
By John Wakerly
Dept, of Electrical Engineering
Computer Systems Lab
Stanford University
Stanford, CA 94305
© 1979, by John F. Wakerly
A couple of months ago I picked up a maintenance manual
for my Lear Siegler ADM-3A terminal. Among the SSI and
silliness in the hand-drawn schematics, I discovered some nice
ways to add some very useful features.
Automatic Repeat
The most useful addition is automatic repeat for every key:
hold down the key long enough, and it starts repeating. Figure
1 shows the schematic for the modification. It requires one
extra chip, a CD4093 quad CMOS Schmitt trigger NAND, to
be added to the board. When I modified my terminal, I found
it convenient to glue this chip in place upside-down on top of
the 74LS00 at location K16 of the ADM-3A circuit board.
The modification also uses a spare 74LS04 inverter already
present in the terminal; the existing trace going to pin 1 of this
chip must be cut as shown in Figure 2. By the way, if you
can’t identify pin 1 of an IC, then you shouldn’t be doing
these modifications.
The few additional components and wires may be soldered
in place between the CD4093, the 74LS04, and nearby
locations. Ground may be picked up from the foil that runs
along the peripheiy of the circuit board or from pin 7 of the
74LS04; +5 is avidlable at pin 14 of the 74LS04. Be sure to
install the diode in the correct direction; the band on the
diode corresponds to the straight line in the diode symbol.
Also, the 4.7 capacitor should be a tantalum or electrolytic,
and the end marked “+” should be connected to the diode-
resistor junction as shown. The circuit may be tested off-line
with the terminal in half-duplex mode (set the HDX/FDX
switch to HDX).
Op eration of the circuit is straightforward. The existing
signal KEYDATA is low whenever any key is depressed, high
otherwise. This signal is buffered through a spare 74LS04
inverter at location LI 6. The 74LS04 drives an RC network
through a diode; any switching diode may be used. The voltage
across the capacitor is sensed by the CD4093 Schmitt-trigger
NAND, whose output is tied in parallel with the ADM -
3A repeat key.
Number 42
56
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E Menlo Park, CA 94305
Page 15
cut here
1
1
[=
—_
c
□
c
□
c
□
[I
L16
□
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B5
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c
□
c
V
□
□
c
c
□
c
=i 4
c
□
c
cut here
Figure 2 Trace cut at LI6.
Figure 3 Trace cut at B5.
Normally, KEYDATA is high, the 74LS04 output is low,
holding the capacitor discharged through the diode, and the
CD4093 o utput is high. When any key is depressed,
KEYDATA goes low, raising the output of the 74LS04 high,
which allows the capacitor to charge through the resistor. If
the key is held down long enough, the input switching
threshold of the CD4093 will be crossed and its output will go
low, mimicking the effect of holding down the repeat key.
When the key is released, the capacitor immediately discharges
through the diode and the 74LS04 low output, causing the
repeat function to be released.
Some notes on this circuit are in order for serious logic
designers. You may ask, why not get rid of the 74LS04 and
just use t he W outpu t of the 74LS151, which is the comple¬
ment of KEYDATA? The problem is that Y is obtained
internally in the 74LS15 1 by inverting W. If we used W, we
would glitch KEYDATA for the rest of the terminal because
of tJie nonstandard voltages that would be developed every
time we discharged the capacitor througi W. Another
question: why not use another section of the CD4093 instead
of the spare 74LS04? Answer: the CD4093 doesn’t have
enough low-state drive to quickly discharge the capacitor.
Finally, why not use another spare 74LS04 instead of the
CD4093? Answer: CMOS is required for its high input
impedance (5M ohms or more) to allow the 80K-ohm resistor
to determine the effective time constant; LSTTL input impe¬
dance is only about 20K ohms. A Schmitt trigger is required
because of the slow input signal rise time.
The length of time a key must be held down before it starts
to repeat is determined by the RC time constant. As a rel¬
atively fast typist, I found an 80K resistor and 4.7 uf capacitor
to gi ve an appropriate delay, about 400 milliseconds. More
heavy -handed t pists will want to increase these values to
prevent unwantc d key repetitions; doubling either component
value doubles th t delay.
Caps Lock
The next mo lification is to eliminate a useless feature and
replace it with a useful one. If you really have found a use for
the keyboard-lock feature of the ADM-3 A, read no further.
Otherwise, eliminate it by cutting the trace coming into the
74LS11 at location B5, pin 10, and connecting pins 10 and 11
of tliis IC together, as shown in Figure 3.
Now the KBLOCK signal can be used to enable and disable
lower case characters. As shown in Figure 4, simply connect a
wire from pin 9 of the 74LS113 at loca tion BIO t o pin 13 of
the 74LS10 at location L10. This puts KBLOCK in parallel
with the LC EN switch on the front panel. Then set the LC EN
switch to the UC posi tion, and the internal DISABLE/
KBLOCK switch to the KBLOCK position. Now when you
turn on the terminal, it will come up in uppercase only. When¬
ever the terminal receives a control-O, lower case will be
enabled; receiving a control-N will return it to uppercase only.
If you connect to pin 8 instead of 9 of the 74LS113, then the
functions of control-N and control-0 are reversed and the
terminal will power-up to lowercase only. Setting the LC EN
switch to LC EN unconditionally selects lower case. As before,
these functions may be tested off-line with the terminal in
half-duplex mode.
If your computer doesn’t echo control characters when
they are typed from the keyboard, you may want to provide
some special system commands to enable and disable lower
case. For example, I modified my computer’s CRT I/O driver
so that whenever it receives a NULL from the terminal
(control-*® or control-space on the ADM-3A), it toggles an
internal upper/lower mode flag and sends the appropriate
control code to the terminal to put it in that mode. Further¬
more, I automatically select uppercase-only when exiting to
my ROM monitor, and enable lower case when entering the
disk operating system.
Page 16
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
57
31 Extra Flavors of Printing Characters
If you have an ADM-3A with the lower case option, you
may notice that sometimes at power-up there are strange
characters on the screen you can never generate yourself.
Well, it turns out that the optional lower case ROM for the
terminal has 64 characters in it, of which 32 are the normal
lower-case character set. The other 32 characters correspond
to the 32 ASCII control codes, 00 through IF hex; 31 of these
are printing characters, including some underlined letters and
numbers, various arrows, a bell, and strange symbols. The
terminal never stores these codes in the refresh memory when
they are received from the computer; it simply performs the
action, if any, required by the control code (clear screen, move
cursor, etc.). Thus, the only time you see these characters is
when they somehow get into the refresh memory at power up.
What we need, then, is a way for the computer to tell the
terminal to go ahead and store these codes.
As wired at the factory, the ADM-3A looks only at the
low-order 7 bits of each received character, even if an 8-bit
character is received. We can make use of the eighth bit to
make the extra characters available. If the eighth bit is a 0, we
treat a character between 00 and IF hex as a normal control
character; if it is a 1, we ignore the control function and store
the character in the refresh memory instead. All this takes is
one spare AND gate at location H5. As shown in Figure 5, cut
the output trace from pin 10 of the 74LS02 at H3 and input
trace from pin 10 of the 74LS25 at HI. Then install four new
wires to make the circuit shown in Figure 6.
Continued on p. 25
Figure 6 Extra-character circuit.
Number 42
58
Dr Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 17
I
IA Table-Driven Assembler
I
BY DARREL J. VAN BUER
1522 Brockton Avenue #5
Los Angeles, CA 90025
Darrel J. Van Buer is studying for a Ph.D. in CS at UCLA.
He is a senior computer programmer analyst at SDC.
This article describes a table driven assembler I recently
constructed to help with my investigation of the new one chip
microcomputers. At present, my interest is in the Intel 8748
computer and the related Intel 8741 Universal Peripheral
Interface, both with user programmable EPROMs. With the
continued proliferation of new microprocessors, especially
low end processors too small for resident utilities, I felt the
best approach was a table driven cross-assembler. Since my
main system is an 8085-based system running CP/M, I had a
large choice of source languages for the assembler. I used
ML,-80 for several reasons, including availability, efficiency
and structured programming features. ML-80 is a structured
assembler/compiler written in 1975 to combine the advantages
of assembler level machine control with a good set of control
structures to produce readable and efficient code. I wrote it
as a table driven compiler to make it easier to modify for use
with other 8-bit machines. In particular, all components of
an operation code except immediate operands are determined
by table lookup alone. The target machines far the assembler
listed here are the Intel 8748/8048/8035 and 8741/8041.
General Features of the Assembler
The assembler provides as basic features for all versions
line parsing, symbol table management and expression evalua¬
tion. The line parser defines a source line as a series of fields
separated by blanks and tabs and terminated by CR6LF.
The first field is an optional label starting in column one,
not over 6 characters long, optionally followed by a colon.
The second field is an operation code not over 5 characters.
The third field is an optional list of operands separated by
commas. The fourth field treats the rest of the line as com¬
ments. Note that, for some operations, some of the optional
fields may actually be required. To allow for longer labels
and operations requires changing the declarations for OP,
LABELL, LABELTAB and adjusting the loop counters in
PARSELINE and GETNAMEVAL. The expiession evaluator
recognizes labels, numbers and *$’ for the current value of the
location counter (i.e., the address of the inslruction contain¬
ing $). Numbers may be in decimal, hexadecimal, octal or bi¬
nary, denoted by a suffix of D, H, O, or B respectively. A
number with no suffix is decimal. The first character of
numbers must always be digits to distinguish them from
labels. The expression evaluator also recognizes the operation
symbols V, *>’ and “<’ for plus, minus, low byte and
high byte respectively. When used as unary operations, the
On CP/M
first operand is zero. Low byte is the less significant byte of
the following value and high byte is the more significant
byte. For example, >01234H is 34H and <01234H is 12H.
Customizing the Assembler
The behavior of the assembler is controlled by two main
tables and two case statements (one in each pass). The first
table in the listing is the operand table from label RR1
through RR31. This table is coded using macros RENTRY,
RERROR, RNULL and RGO. The second table is in the
declaration of OTAB immediately after the operand table.
This table, constructed with the macro OENTRY, describes
the operation codes for the assembler. Each entry in this table
gives an operation code, e.g., ‘ORG’, the base value for this
operation, e.g., ’0‘, and names a starting point in the operand
table, e.g., ‘RR30’. Each operation is applied to a serial search
of this table for an exact match (both length and contents),
the operation value is saved and the operand pointer is used to
start the search for operands. The operand table is serially
searched from the starting point given by the operation table.
The operand table contains several kinds of entries, some of
which exist to make the table shorter by sharing portions.
Entries created by the macro RENTRY result in comparison
of the start of the operand field with the table entry. An
RENTRY consists of match string, e.g. ‘PI, #’, an operation
correction value, e.g., ‘49’ meaning 49H, which is added to the
opcode to produce the correct value for this operand, and
a type code, e.g. ‘LIM]’, which drives the case clauses for
operand format in the assembler. These types are generated
by macros which expand to small numbers. The types which
are currently defined are error, immediate byte follows, same
page branches, full memory call/jump, pseudo operation and
operand complete. The actual meaning of a type is defined
by the case statements in PASS1 and PASS2 described below.
Entries created by the macro RNULL are for operations
which have no operands. An entry or type RNULL is identical
to RENTRY with null match string. Since the search is for a
match on the first few characters of an operand, if one op¬
erand form is a prefix of another for the same operation
(say P and P3) the longer one should come first, otherwise
both P and P3 would match with P.
Entries created by the macro RGO are used to share parts
of the operand lists. An RGO entry gives an opcode correction
value and names another part of the operand table. When the
table lookup routines encounter an RGO entry, the search
Page 18
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
59
switches to the named part of the table after adding the cor¬
rection value to the opcode. This correction allows for differ¬
ences in the spacing of different opcodes. For example, the
table entry RR4 ends with [RGO ‘60’ ‘LRR3]’] because
most of the possible operands for ADD are the same as for
XCH, saving 10 entries. RR3 is part of another space saving
technique. RR3 is an internal label or the declaration for RR1
(and RR2), thus, if the search falls through the entry efter
RR2, the effect is the same as LRGO ‘0’ ‘LRR3] ’ ] without
the overhead. RGO allows several variants to join since only
one can fall through, and also allows other variants by using
opcode corrections.
The last type of entry is generated by the RERROR macro.
This macro signals that the operand field does not contain
a valid entry. Note that every path through the operand table
must end with RERROR or RNULL.
PASS1 Case Statement
This assembler is a traditional two pass assembler which
resolves label values on the first pass and generates code on
the second pass. These two passes are embodied in the pro¬
cedures PASS1 and PASS2. In each of these procedures, a
case statement is driven by the results of the operand table
search. In pass one, the case alternatives do processing to
resolve all labels. The basic function of pass one defines all
labels as the current value of the location counter (the location
counter is the assembler’s analog of the processor’s program
counter). The main function of the case statement is to in¬
crement the location counter by the length of each instruction.
The second function is to provide special processing for
pseudo operations. Pseudo operation processing is driven by
a second case statement. The driving value for this case state¬
ment is the opcode value since pseudo operations don’t
generate an operation in the usual sense. The case for EQU
modifies the definition of its label to the value of the expres¬
sion. The case for ORG resets the location counter to its
expression. The DS case increments the location counter by
the value of the expression.
PASS2 Case Statement
The main action in pass two is code generation by the dif¬
ferent cases with appropriate location counter adjustment
(normally done by EMIT1, the subroutine which emits a byte
of code), again with special processing in a second case
statement for pseudo-operations. The calls to MAGNITUDE-
ERROR are made when a two byte value is to be emitted in
one byte but is not the sign extension of the single byte.
8741/8748 Assembler Notes
The language currently recognized by the assembler is the
union of the operations for the Intel 8741 and 8748, and the
appropriate Intel User’s Manuals are the primary reference
on valid formats and operands. The operations are divided
into four types for this assembler.
Type 1. This type is for operations with a single immediate
operand data byte, for example ADD A, #5.
Type 2. This type is for the short conditional jump instruc¬
tions which are limited to destinations on the same page (256
byte block) as the next instruction, for example DJNZ Rl,
LOOP.
Type 3. Tliis type is for call and jump in which three
address bits are part of the opcode and the remainder of the
address is in a second byte.
Type 4. Tliis is a dummy type for pseudo operations.
These are
ORG
expression
;set location counter to ex¬
pression
label
EQU
expression
jequate label to expression
Llab]
DS
expression
p-eserve expression bytes
Llab]
DB
expression
;define byte with value ex¬
pression
PRINT
ON
;list assembly to printer
PRINT
OFF
pio listing (except errors)
Most of these are standard pseudo operations. The PRINT
pseudo operation immediately affects the listing, making it
possible to list only parts of an assembly. The initial state of
the assembler is PRINT ON.
Type 5. This case is for simple opcodes with operands
included within a single byte, for example MOV A, @R1.
Miscellaneous Considerations
As compiled here, the assembler is limited to 255 labels
by the table size declaration, but the search strategy is general
enough for any length table. To simplify I/O, the assembler
also presently uses the fact that there is only IK of EPROM
in an Intel 8748/8741, and first generates an in-memory array
of the result and fianlly writes a binary file of the result.
For larger memories, such as an 8080, EMIT1 needs to be
revised to write to an output file, in a format such as Intel
hex. Since I wrote this on my CP/M system, the I/O used is
specific to CP/M but has been carefully encapsulated in only
a few subroutines. Procedure GETFC returns successive char¬
acters from the input file, and thus is responsible for reading
disk sectors and dribbling the contents out one character at
a time. Procedures PRINTALINE and PRMSG call CP/M
BDOS to type characters on the console. PRINTALINE
lists lines of formatted assembly output, while PRMSG types
error messages. The procedures ZTFCB, OPENR and OPEN-
HEX also perform CP/M specific functions. These procedures
all assume the existence of a CP/M initialized file control
block which CP/M has parsed the required file name from the
command invoking the assembler. For another DOS, it may be
necessary to do this parsing separately, and change the format
assumptions made by these routines. ZTFCB initializes a file
control block piior to opening. OPENR opens a file control
block to read the source file, and is called twice, once for
each pass. OPENHEX creates a new file with suffix SCC and
writes the memory image buffer of the assembled code out in
binary format. Outside of these routines, the assembler makes
no assumptions about the file structures available except that
it is a sequence of bytes which can be read twice. Conversion
to another DOS should be fairly easy, and conversion to a
non-disk system should also be feasible.
Program Availa bility
The ML-80 compiler is part of the CP/M users group col¬
lection, and so is available from them. The PL/M source
for ML-80 is available from the Intel Users’ Group. As an
alternative, for $10 I will provide an 8 inch, single density
IBM format CP/M diskette which contains ML-80 and the
source for the assembler in this article.
Number 42
60
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 19
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Dr. Dobb's Journal of Conputer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
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Number 42
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
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Number 42
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
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Now the computer can display the 31 extra characters by
sending codes 81 through 9F hex to the terminal (code 80 will
print as a space). All we need now is a way to generate these
codes from the terminal itself. Again, the terminal normally
generates only a 7-bit code; bit 8 is set according to the value
of the BIT8 0/1 switch when sending 8-bit data. As shown in
Figure 7, we can instead use the otherwise useless HERE IS
key to set bit 8 from the keyboard. The signal at pin 12 of
the 74LS04 at location L16 is high whenever HERE IS is
depressed. Simply connect this signal the UART bit 8 input
(pin 33 of K5) and set the BIT8 0/1 switch to 1. Now bit 8
will be set to 1 only when HERE IS is depressed. Thus,
pressing both CTRL and HERE IS will access the extra
characters. If you are especially lazy, you can make HERE
IS automatically invoke the CTRL function also, by con¬
necting pin 13 of the 74LS02 at L12 to pin 9 of the 74LS04
at L16,and grounding pin 6 of the 74LS04 at L18.
Acknowledgments
Thanks go to Dennis Allison for suggesting that I make
these enhancements available to DDT s readers, and for serving
as a guinea pig for the do-it-yourself instructions given above.
This article was prepared using my ADM-3A.(note
the use of the repeat key) and custom word-processing
software running under Smoke Signal Broadcasting’s DOS68
disk operating system for the Southwest Tech 6800 computer
system.
+5
Figure 7 Modifications to set bit 8.
Number 42
66
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 25
A User Interface to
Program
Renumbering
BY DEWITTS. BROWN
1650 9th Ave. S.E.
Rochester, MN 55901
In DDJ #23, Steve Wozniak detailed the theory and code
necessary to renumber BASIC programs on the APPLE-II.
Although Wozniak’s program was functionally good, I could
not use it with the interface provided. In this article I would
like to explain my solution. If you have an APPLE-II com¬
puter or are a forgetful, lazy user, read on.
The Goal
Modified User Interface
An early solution to this problem used variables and an
EXEC file to reduce the typing and remembering necessary.
Renumber Data Set Range
>NEWSTART = 150
>NEWINC = 10
>RSTART= 100
>REND= 110
>EXEC RENUM. RANGE
Renumber Whole Data Set
>NEWSTART = 150
>NEWINC = 10
>EXEC RENUM .ALL
Renumber lines 100-110, to start at 150, spaced by 10.
Original User Interface
>BLOAD RENUMBER.ASM
>Poke 2,150 Mod 256
>Poke 3,150/256
>Poke 4,10 Mod 256
>Poke 5,10/256
>Poke 6,100 Mod 256
>Poke 7,100/256
>Poke 8,110 Mod 256
>Poke 9,110/256
>CALL 776
This is too much typing (about 160 keystrokes for this
example) and too much remembering (the meaning of four
locations in memory and two call addresses) for forgetful, lazy
me.
This approach still requires 60 keystrokes and the remem¬
bering of four variable names and two exec file names (because
meaningful names are used in place of numbers, the memory
part is easier than the original user interface).
Ideal User Interface
Even with the modified user interface, the renumber
program was too cumbersome to use often. I, therefore,
decided to create the “ideal user interface” to the renumber
program. Here are the qualities I set as “ideal.”
1. Minimal typing required — only the actual input value
should be entered.
2. Only one name to remember — that name would be
meaningful to aid in remembering it.
3. Where defaults were used, they would be listed — the actual
default would be selected with a simple “return.”
4. Some degree of bad typing would be allowed — the user
could correct mistakes until “return” entered.
Page 26
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
67
5. Some degree of error checking would be imple¬
mented — numbers too big or non-numeric characters
should be rejected.
6. Performance and storage impacts to the program being
renumbered should be negligible — the renumber program is
a tool, not a goal.
Here is the ideal user interface:
>EXEC RENUM
Commands in RENUM are
HIMEM:-27648
RENUM=-27648
BLOAD RENUM.ASM.A$9400.L$200
CALL RENUM
On a cleared screen, APPLE responds
( ENTER LINE NUMBER DEFAULT
NEW START
NEW INCREMENT
RANGE START
RANGE END
100 -»150
103-► 160
106 -> 170
107-»180
109 -*• 180
110 -> 190
100
100
0
65535
? 150 (RETURN)
? 10 (RETURN)
? 100 (RETURN)
? 110 (RETURN)
♦
Entered by
user.
Subsequent renumbers could be done by typing ‘CALL
RENUM’ to avoid diskette I/O delay (of course, continuing to
type ‘EXEC RENUM’ would work as well—just slower).
This solution requires only 25 keystrokes (15 if all defaults
taken) and requires the user to remember 1 easily-remembered
name. Quantitatively, this user interface is 6 times better than
the original interface.
Evaluation
The goals set down for the ideal user interface were met,
except for the impact on storage. Compared with 190 bytes
(X’BE’) used originally, 512 bytes (X’200’) are used. Also,
the original version did not take storage from the program
area, as this version does.
My solution is break a very large program into pieces to
allow room for this version of renumber. The pieces could
be connected using the ‘chain’ command. This solution en¬
courages me to keep program development modular, as
advocated in structured programming.
References
1. Auricchio, Rick. "An Apple-ll Programmer's Guide," The Best of
MICRO, Volume 1
2. Synertek. "SY 6500/MCS 6500 Microcomputer Family Program¬
ming Manual." Synertek, Santa Clara, CA (May, 1978)
3. Wozniak, Steve. "Renumbering & Appending BASIC Programs on
the APPLE-II Computer." Dr. Dobb's Journal of Computer Calis¬
thenics & Orthodontia, Number 23 (March, 1978)
4. Wozniak, Steve. "SWEET16: The 6502 Dream Machine" Byte
Magazine, (November, 1977)
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
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Number 42
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
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Number 42
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(Continued on page 33 )
Number 42
72
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Pacie 31
CONVERTING BINARY
TO DECIMAL
BY DENNIS ALLISON
H39 Spruce Street
Atherton, CA 94025
Dennis R. Allison is an independent consultant and
part-time lecturer at Stanford University’s Computer
Systems Laboratory. His research interests include
programming languages and their relationship to pro¬
blem solving and creativity. He is presently President
and Chairman of the Board of Trustees of the People’s
Computer Company. He is a member of ACM, SIAM,
and IEEE and serves as an Associate Technical Editor
of the IEEE Computer Society’s general membership
publication, Computer Magazine.
Every system needs to have some medmnism for output¬
ting data in a form easily useable by humans. With our ten-
finger heritage, the easy-to-generate hex, octal, and binary
displays are inadequate, particularly for non-specialists. This
note describes a conversion routine suitable for use with
microprocessors as it does not use either multiplication or
division. For a more comprehensive treatment see Knuth’s
Seminumerical Algorithms (Addison-Weslev, Reading, MA,
1969).
There are several slightly different problems which have
to be solved. For a decimal output to a terminal, we normally
want a zero-suppressed output to have the number 2 print
a “2” and not “00002”. On the other hand , if the output is
to go to a LED display which normally outputs hex, the con¬
version must be to packed decimal, not characters, and should
not be zero suppressed. The idea is pretty much the same for
each, however.
The routine depends upon being able to compute both the
quotient and the remainder after dividing by 10, is the right¬
most digit. And n/10 contains all the digits to the right.
This observation suggests the routine
prdec ( n ) int n. |
int q, r; /* locals for quotient and re¬
mainder */
if (n < 0) | putchar(' — n = —n; 1
q = n/10;
r = n % 10;
if (q ! = 0) prdec(q); /* print digits to the
left */
| putchar(r + ' 0 ');
written in the programming language C, which performs a
binary to decimal conversion with zero suppression. The pro¬
cedure is recursive, so local variables are allocated on the
stack. The digits are constructed right to left and printed
left to right. The subroutine stack is used to reverse the con¬
verted number. Signed numbers are converted to unsigned
numbers following output of a sign.
If one does not want to suppress zeros, one can add another
parameter to the call, the number of digits desired.
If one does that the program becomes
prdec ( n,dig) int n,dig; {
int q,r; /*locals for quotient and re¬
mainder */
if (dig < = 0) return;
if (n < 0) { putchar(' - '); n = -n; }
q = n/10;
r = n % 10;
prdec(q,dig— 1); /* print digits to left */
putchar(r + '0');
Page 32
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
73
If one wants a packed decimal representation for positive
numbers only, as would be the case for a LED display, the call
to character output routine, putchar, should be replaced with
a call to a packing routine which simply masks off the decimal
digit and shifts it left four bits. One way to do this would
be to have a global 16-bit variable and use a C routine of
the form
pack ( dig ) int dig; {
packed = (packed < <4)&(dig& 017));
Unfortunately both these routines fail for the largest possi¬
ble negative number because of the way the PDP-11 handles
the remaindering process. The division must be unsigned for
the algorithm to work. Remember that 2’s complement num¬
bers have an asymmetric range skewed to the negative side.
For example, 2’s complement 4-bit numbers represent values
from -8 to +7. And negating the largest possible negative
number gives the largest possible negative number.
If we are going to implement this procedure, we need a way
to do the division and remaindering operation. Strangely
enough, we do the division using multiplication by 0.1. The
fraction 1/10 has a binary representation
1/10 =
0.0000110011001100110011001100110011001100 ...
which may be thought of as a sum of fractions
1/10 = 1/16 + 1/32 + 1/256 + 1/512 + ...
The fraction will never represent the correct value. If we
truncate the representation at any point it will always be too
small. If alpha is an approximation to 0.1 which is too small
by 1/w, one can write
(alpha + 1/w) * u = u/10
which suggests that
alpha * u = u/10 - u/w
Now the error in the representation, 1/w will always be less
than or equal to the smallest value represented in the fraction
alpha. The value of the ratio u/w will always be less than or
equal to one. Thus, we can write a division by ten routine
which also computes the remainder and uses only shifts and
adds. Using the C notation of » for right shift one has
int rem; /* global to catch value of remainder */
divlO ( x ) int x; |
int u,v;
u=(x» 1) + (x»2) + (x»5) + (x»6) + (x»9) +
(x» 10) + (x» 13) + (x» 14);
u = »3;
v = mull0(u);
if( (rem = x - v) > = 10) | u++; rem = rem - 10;}
j return (u);
This program uses right shifts to implement division so it
won’t work for negative numbers. The same problem with the
largest negative number will also appear unless the right shift is
implemented as a logical right shift rather than an arithmetic
right shift which sign extends.
The second to the last line corrects the quotient and
remainder when the value computed is in error by one.
One now needs to have a simple multiplication by ten
routine. This can be done with a few temps and additions.
In C the routine looks like
mull0(x) int x; {
int t;
x = x + x;t = x + x;t = t + t;
return (t+x);
which works by noting that 10*x = 8*x + 2*x and using
addition to do the multiplication by two.
Mapping these routines into machine language is left as
an exercise for tie reader. The only problem is how to repre¬
sent local variables in the recursive procedures. For most
microprocessors local variables may be implemented on the
subroutine stack. At subroutine entry the stack pointer is
decremented by the number of bytes needed for local
variables. Locals are then accessed by indexing from the stack
pointer. Just prior to subroutine return the stack pointer must
be incremented to readjust it so the return address is at the
top of stack.
And, of course, there are equivalent non-recursive programs
which use exactly the same ideas but keep their own stacks.
They require slifjhtly more code and data space but may run
faster.
(continued from page 3 1)
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Number 42
74
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Page 33
UCSD PASCAL
Terminal Parameters
BY RONALD G. PARSONS
9001 Laurel Grove Dr.
Austin, TX 78758
The PASCAL system from the University of California at
San Diego has a very useful system generation procedure by
wliich the physical parameters of the user’s screen and termi¬
nal may be defined to the system. These parameters include
the keyboard cursor keys, the screen cursor movement char¬
acters, and such entities as the characters to clear the screen
and erase to the end of the line. These parameters are defined
for the system by using a supplied program SETUP and are
stored on a file named SYSTEM.MISCINFO.
In order to write programs which are as independent as
possible of the user’s screen and keyboard configuration,
these parameters must be known to the program. For example,
if you wish to write a program which must be able to move
the cursor around on the screen and always stay inside the
user’s screen whether it is 64 X 16 or 80 X 24, the cursor
controls and screen size must be known. The record definition
and initialization procedure below may be used to make these
pa rameters known to a user-written program. The main pro¬
cedure illustrates the use of the parameters in the record.
There is only one oddly defined parameter—“verticalm-
delay”— which tells the number of nulls to be sent after a
vertical cursor move. This variable is defined here as character,
but should be used as an integer. The statement
intverticalmdelay : = ord(verticalmdelay) ;
will transform the quantity to an integer.
I hope the way UCSD PASCAL lets the user define his
system parameters to the operating system will be widely
copied. 1 wish UCSD had been consistent in their use of these
pan meters in setting the length of their prompt lines which
often overflow a 64 character screen line.
Program testmiscinfo;
SYSTEM.MISCINFO parameter record definition
Author: Ronald 0. Parsons
Date: August 21, 1979
Defines terminal and screen parameters from the file
produced by SETUP for UCSD Pascal Version 1.5.
The following variables are associated with
the SETUP defined parameter.
The full name of these variables is minfobuffer.xxxxx
e.g.,
minfobuffer.screenhelght
or
with minfobuffer do ... screenhelght ... end;
The following variables are type Boolean.
hasclock
has8510A
haslowercase
hasrandom
hasslow
student
premcup
premcrlght
preereol
preereos
premchome
predcharacter
preerscreen
preerline
prekmcright
prekmcleft
prekmcup
prekmcdown
prenonprintchar
prekeystop
prekeybreak
prekeyflush
prekeyendfile
preedescapekey
prekeydline
prekeydcharacter
preedacceptkey
HAS CLOCK
HAS 8501A
HAS LOWER CASE
HAS RANDOM CURSOR ADDRESSING
HAS SLOW TERMINAL
STUDENT
PREFIX [MOVE CURSOR UP]
PREFIX [MOVE CURSOR RIGHT]
PREFIX [ERASE TO END OF LINE]
PREFIX [ERASE TO END OF SCREEN]
PREFIX [MOVE CURSOR HOME]
PREFIX [DELETE CHARACTER]
PREFIX [ERASE SCREEN]
PREFIX [ERASE LINE]
PREFIX [KEY FOR MOVING CURSOR RIGHT]
PREFIX [KEY FOR MOVING CURSOR LEFT]
PREFIX [KEY FOR MOVING CURSOR UP]
PREFIX [KEY FOR MOVING CURSOR DOWN]
PREFIX [NON-PRINTING CHARACTER]
PREFIX [KEY FOR STOP]
PREFIX [KEY FOR BREAK]
PREFIX [KEY FOR FLUSH]
PREFIX [KEY TO END FILE]
PREFIX [EDITOR ’ESCAPE’ KEY]
PREFIX [KEY TO DELETE LINE]
PREFIX [KEY TO DELETE CHARACTER]
PREFIX [EDITOR 'ACCEPT* KEY]
- The following variables are type integer.
screenhelght SCREEN HEIGHT
screenwidth SCREEN WIDTH
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Page 34
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
75
(•
variables are type char.
*)
(•
leadintoscreen
LEAD-IN TO SCREEN
•)
(*
movecursorhome
MOVE CURSOR HOME
*)
(•
eraseeos
ERASE TO END OF SCREEN
*)
(*
eraseeol
ERASE TO END OF LINE
•)
(•
movecright
MOVE CURSOR RIGHT
•>
(*
movecup
MOVE CURSOR UP
•>
(*
backspace
BACKSPACE
•)
c*
verticalmdelay
VERTICAL MOVE DELAY
•>
(*
eraseline
ERASE LINE
•)
(•
erasescreen
ERASE SCREEN
•)
(•
keytomcup
KEY TO MOVE CURSOR UP
*)
(*
keytomcdown
KEY TO MOVE CURSOR DOWN
•)
(•
keytome left
KEY TO MOVE CURSOR LEFT
•)
(*
keytomcright
KEY TO MOVE CURSOR RIGHT
*)
(*
keytoendfile
KEY TO END FILE
•)
(*
keyforflush
KEY FOR FLUSH
•)
(•
keyforbreak
KEY FOR BREAK
•)
(*
keyforstop
KEY FOR STOP
*)
(•
keytodcharacter
KEY TO DELETE CHARACTER
*)
(*
nonprlntchar
NON-PRINTING CHARACTER
*)
(•
keytodline
KEY TO DELETE LINE
*)
(*
editorescapekey
EDITOR 'ESCAPE' KEY
•>
(•
leadincharacter
LEAD-IN CHARACTER FROM KEYBOARD
•)
(•
(*
editoracceptkey
EDITOR 'ACCEPT' KEY
•)
*)
(
)
type
miscinforec ■ packed record
dummyl : packed array [0..28] of integer;
dummy2.dummy3,student,hasslow.hasrandom,haslowercase,
has8510A,ha8clock : Boolean;
dummy: integer;
erasescreen,era8eline.verticalmdelay.backspace,
movecup.movecright.eraseeol.eraseeos.movecursorhome,
leadintoscreen : char;
preerline.preerscreen.predcharacter.premchome,
preereos.preereol.premcrlght,premcup : Boolean;
screenwidth.screenhelght : integer;
editoracceptkey.leadincharacter,editorescapekey,
keytodline,nonprintchar.keytodcheracter,
keyforstop.keyforbreak.keyforflush,keytoendfile,
keytomcright.keytomcleft.keytomcdown.keytomcup : char;
dummy5 : integer;
dummy6.dummy7.preedacceptkey.prekeydcharacter,
prekeydline,preedescapekey.prekeyendfile,
prekeyflush,prekeybreak,prekeystop.prenonprintchar,
prekmcdown.prekmcup.prekmcleft.prekmcrlght : Boolean;
dummy8 : packed array [ | *8..95] of integer;
end;
var
mlnfobuffer : miscinforec;
procedure minfoinit; (* Initialize •)
var
minfoflle : file of miscinforec;
begin
reset (minfoflle,'•SYSTEM.MISCINFO');
get (minfoflle);
mlnfobuffer minfoflle ;
close (minfoflle);
end;
begin
minfoinit;
with mlnfobuffer do
begin
writeln(* Lead-in to screen - '.ord(leadintoscreen));
writeln(* Cursor home ■ ',ord(movecursorhome));
vrriteln('Erase to end-of-screen ■ ' .ord(eraseeos));
writeln('Erase to end-of-llne ■ '.ord(eraseeol));
wrlteln('Move cursor right ■ ',ord(movecright));
writeln('Move cursor up ■ '.ord(movecup));
writeln('Key to end file ■ '.ord(keytoendfile));
writeln('Key to move cursor up ■ '.ord(keytomcup));
writeCHas clock - ');
if hasclock then writeln('T') else writeln('F');
write('Has 8510A - ');
if has8510A then writeln('T') else writeln('F');
writeCHas lowercase * ');
if haslowercase then wrlteln('T') else writeln('P');
writeCHas random • ');
if hasrandom then writeln('T') else wrlteln('F');
writeCHas slow - ');
if hasslow then writeln('T') else writeln('F');
wrlte('Student * ');
if student then writeln('T') else writeln('F');
write('PRE [key to move cursor up] ■ ');
if prekmcup then writeln('T') else writeln('F');
writeln;
writeIn(screenhelght,» ',screenwldth);
gotoxy((screenwidth div 2),(screenheight div 2));
(• go to center of screen *)
write('Input "return" to clear screen');
readln;
write(erasescreen);
end;
end.
Number 42
76
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E Menlo Park, CA 94025
Page 35
PASTIMES '
AND
PLEASURES
BY CHARLES WETHERELL
© 1979, Charles Wetherell
Four Famous Programs
Programs are not always interesting because of their output;
sometimes the program itself is the object of interest. This
month I am going to describe four famous programs which
fall into this class. Even if you don’t actually write versions
for your own computer, thinking through each program will
surely reward you with deeper understanding of your
computer.
I Got Plenty of Nothin’
The first problem is to clear memory to zero. Easy enough,
you say—just hit the CLEAR button. But the: rules are a little
more complicated. All of writable memory must be set to zero
at program completion; as an added fillip, all registers should
be zero as well. The program must execute normally without
using any input/output device and without any operator inter¬
vention. If possible, the program should halt normally. As an
example, I know of one computer which used a store double
word zero instruction to wipe out the last two words of a
loop through memory. An even harder problem is to store a
preselected bit pattern throughout memory. You may find
this program is not possible for some bit patterns.
Stamina
Now consider the problem of writing the longest running
program you can. The same rules apply—no I/O, no operator
intervention, normal program execution. How about infinite
loops? Well, my definition of a loop may be a little different
than yours. I will say the program loops when the same main
memory configuration occurs for the second time. The repeti¬
tion must be exact, bit by bit. To make things simple, you
may specify any starting memory configuration you like. Your
program must reside in main memory and count as part of the
memory pattern. Strangely enough, almost every computer has
the same solution for this problem; I will suggest it at the end
of the column.
Introspection
For the third problem, consider a program which can
describe itself. Specifically, the introspective program must
print out an exact listing of its source coding. You are not
allowed to use any tricks. For example, you may not reread
the source input. Some compilers and interpreters leave copies
of source lying around in memory. You may not reach in and
print such a source. The only resource you are allowed is the
program itself. A memory dump does not constitute a source
listing.
The introspective program is particularly interesting
because it is always possible. In any language—FORTRAN,
BASIC, PASCAL, assembly—as long as the language is
“sufficiently” powerful—the program will exist. Every normal
programming language is powerful enough; see the column on
Ackermann’s Function (DDJ # 37) to find out how powerful
is “powerful.” The existence is a consequence of the
Recursion Theorem. Fortunately, you can solve this problem
without using any mathematics. Hint: the solution hinges on
the proper use of quotation.
A Pox On You
The last program is the computer virus. Before you do any
work on viruses, you better be sure that you either have a
“clean room” or can stand to take the consequences. If you
are certain, I’ll go on.
Page 36
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
77
The virus is a program which implants itself into another
program, subverts the host’s operations, creates multiple
copies of itself, and then implants the copies into other
victim programs. Obviously, once a virus gets loose in a
system, the system will soon spend all its time breeding more
viruses. If the fever attacks some common utility like the
compiler'or file manager, the plague may kill the system
immediately. Eradication of a successful virus could be very
difficult.
I know of one rumored virus. Back in the early days of
computing, the 7094 operating system stored all object
programs waiting to be punched onto a single tape. The virus
would read the last object file off the tape, modify it to
include a copy of the virus, and then write the object back
onto the tape. When the object, which would be a single
routine from some other program, was loaded and executed,
the virus would propagate again. Indeed, since object decks
could be physically loaded with several programs, the virus
might be propagated by the unsuspecting owner of the sub¬
routine-a sort of Typhoid Mary. Security features on most
modern systems would defeat this ploy, but it is thinking
about such pathologies that makes designers improve security.
I might add that releasing a virus would certainly be unethical,
if not criminal.
One other rumored virus caused a genetic defect in its
host. The creator of a timesharing system also had a hand in
writing the compiler for the language in which the entire
system was written. He modified the compiler so that when¬
ever the SIGN-ON program was compiled, the compiled
SIGN-ON procedure would always recognize his name. This
way he could run on any version of the system anywhere.
Not only that, but if this defect was removed from the
compiler source code, the compiler automatically reinserted
the flaw in the compiler object modules when the old (flawed)
compiler—the only one available, of course—was used to
recompile the new (clean?!) compiler sources. I heard this
tale far removed from the perpetrator and I suspect it to be
apocryphal. But have you checked you compiler lately?
Hint
The longest running program generally treats all of memory
as a giant binary counter and simply increments constantly by
1. When the counter overflows, all memory configurations
(almost) will have been counted off. A sophisticated version
will also move the program around in memory to get more
configurations (only one move is necessary—why?). Don’t try
this program and expect to see it finish; on a computer with
n bits of memory, the program will run for at least 2 n or so
cycles..
Number 42 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
78
Page 37
BY GRIFFITH HAMLIN, JR. AND THOMAS CROCKETT
Los Alamos Scientific Laboratory
Los Alamos, New Mexico 87544
ABSTRACT
GRAF80 is a small scale graphics system designed to
demonstrate some of the capabilities offered by micro¬
processor-assisted graphics. As such, it employ s both hardware
and software techniques. The system implements in a micro¬
processor a ubset of the features of the S1GGRAPH-ACM
CORE (1) graphics package, including picture segmentation
and a subset of the output primitives and primitive attributes.
INTRODUCTION
GRAF80 is a graphics system that uses inexpensive micro¬
processors to enhance the capabilities of a Tektronix storage
tube display. For a fraction of the cost of a Tektronix 4014,
several features can be added that considerably increase its
usefulness. These features include a selective erase using the
segmented display file concept of the SIGGRAPH CORE
graphics package, and the ability to display a limited number
of vectors in refresh mode using a high-bandwidth hardware
interface between a microprocessor and the Tektronix 4014.
HARDWARE
The hardware consists of an IMSAI 8080 microproces¬
sor, which forms the heart of the system; a Tektronix 4014
direct-view storage tube terminal, which is used as the
© 1978, SIGGRAPH-ACM. Reprinted by permission.
graphical output device; and a host computer. The IMSAI
8080 acts as a dedicated device driver, and has software that
supports picture refreshing and segmentation. Any one of
several other available 8-bit microprocessors could be used as
well. Several possibilities exist for interconnecting the micro¬
processor, Tektronix terminal, and host computer. Figure 1
shows one possibility that uses commonly available
equipment.
The Tektronix 4041 has a built-in serial interface that will
support serial communications up to 9600 baud with the
microprocessor. This rate should be sufficient to provide
interactive access to images stored in the microprocessor’s
segmented display file. It is not sufficient to refresh images
using the write-through mode of the 4014. To remedy this,
we have constructed a simple parallel interface to the 4014
and connected it as shown in Figure 2. This interface consists
of only nine 16-pin integrated circuits mounted and wire-
wrapped on a blank Tektronix plug-in card. This provides
one-way byte parallel transmission at the Tektronix 4014
MINIBUS® speed (9 jus/byte) from the microprocessor to
the Tektronix 4014. Communication from the Tektronix 4014
uses the normal serial interface in the 4014 and is connected
directly to the host computer.
Any machine capable of producing GRAF80 commands
may be the host computer. This could be the same or another
microprocessor, a minicomputer, or a large mainframe. In our
case a PRIME-300 minicomputer is used.
Pag/3 38
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
79
SOFTWARE
Software for GRAF80 consists of two main components,
one on each computer. The microprocessor component
receives graphic commands, stores them in a segmented data
structure, and interprets them to produce either a refreshed
or a stored image on the 4014. The host computer software
consists of a package of Fortran subroutines that issue the
commands.
Microprocessor Software
Software for the microprocessor is written in PL/M, a high-
level language designed for microprocessors (2). The software
is designed to intercept and interpret a set of primitive
graphical commands. It requires 4000 bytes of microprocessor
memory plus buffers for the segmented display data structure
generated from the commands. These commands consist of
move and draw graphic-output primitives, along with com¬
mands to OPEN, CLOSE, DISPLAY, and ERASE individual
image segments. The complete list is given in Appendix A.
They were selected from the SIGGRAPH-ACM CORE
graphics package.
The main program consists of a loop that continuously
monitors an I/O subtask and a graphics subtask. (The term
“task” is used to indicate that these two processes could be
executed in parallel if properly synchronized, although they
have been implemented sequentially here. The net effect
would be similar in either case.) When the main loop
determines that a particular task has work to be done, it
transfers control to that task, which runs to completion and
returns to the main loop.
Input to the microprocessor is interrupt driven. A simple
interrupt routine receives a character and stores it in a circular
buffer. The job of the I/O task is to empty the buffer and
evaluate its contents. In order to allow ordinary (nongraphical
or graphical) use of the terminal, a “transparent” mode is
defined. Transparent mode defaults until a special graphics
notify character (ASCII ETB) is received. The I/O task
examines each character and sends it directly to the terminal
until an ETB is encountered, at which time further data is
considered to be graphical. The graphical input is filtered
according to a predefined transmission format (Appendix B)
and stored as a picture segment. When the input buffer is
emptied, control returns to the main loop.
The graphics task serves as an interpreter, converting the
commands stored by the I/O task into device-dependent
instructions which are sent to the 4014 to generate the
picture. By redefining this task, different devices may be
handled within the framework of a single system. Each call to
this device driver interprets a single picture segment; repeated
calls with the same segment allow the refresh capability. The
graphics task returns to the main loop after once interpreting
each segment that needs to be displayed.
Picture segmentation is handled at a level above the device
driver. A number of graphics commands are used for
manipulating segments. The I/O task intercepts these and
takes appropriate action, such as setting flags, allocating
storage, etc. The actual picture commands (or “primitives”)
are stored in the microprocessor’s free memory as one or more
64 -byte blocks, linked together by a forward chain, one chain
per segment. A set of memory management routines is
available to manipulate this data structure. Memory allocation
is automatic and dynamic, implying that each segment receives
only as much memory as it requires. The total amount of
information that may be displayed simultaneously is thus
limited by the amount of memory available to the micro¬
processor. Although the current implementation uses only
real memory, this need not be the case; nonrefreshed segments
could use an auxiliary disk, but system performance would be
somewhat degraded. Currently up to 16 segments may be
defined.
Commands for manipulating segments are listed below.
OPEN(N,R) Opens segment N. All subsequent graphic
primitives become part of the segment
until a matching CLOSE is encountered.
R = refresh status; 0 = no refresh; 1 =
refresh.
CLOSE(N)
DISPLAY (N)
ERASE(N)
DELETE(N)
Closes segment N. No further information
may be added to this segment.
Causes segment N to be displayed.
Removes segment N from the display,
but the segment may be redisplayed later.
Deletes segment from microprocessor
memory.
Open segments may not be nested or overlapping; no more
than one segment may be open at any time. No portion of a
segment is visible until an explicit DISPLAY command is
given, and a currently open segment cannot be displayed. This
differs from the SIGGRAPH-ACM CORE system which
specifies that portions of the open segment become
immediately visible as they are defined. Due to the existence
of both stored and refreshed segments in our implementation,
we departed from the SIGGRAPH CORE here in order to
considerably simplify the microprocessor software.
Erasing a segment merely removes it from the display; it
remains available in the microprocessor memory for further
use. A DELETE command destroys the segment entirely.
Refreshing, as pointed out, is accomplished by the graphics
task; successive iterations of the main program loop refresh
the segment. Since the I/O task usually is not busy, the
graphics task becomes the limiting factor in providing flicker -
free refresh. Within that task two considerations limit the
refresh capacity:
1. the rate at which graphic commands can be interpreted
into Tektronix code by the microprocessor,
2. the drawing speed of the Tektronix 4014 (about 190 qs/in.
which is rather slow for refresh purposes).
I/O time is negligible because of the parallel interface.
Currently the flicker-free refresh capacity is approximately
75 characters or 65 inches of 2-inch vectors (including both
dark and written vectors). This is about half the capacity of
the Tektronix 4014 and is limited in our current implementa¬
tion by the microprocessor software. Different software,
discussed in the last section, should remedy this situation.
Number 42
80
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 39
CONCLUSIONS
Serial 9600- Serial Line,
baud line Data rate
usually determined
by host computer.
Fig. 1. Basic hardware configuration.
Fig. 2. GRAF80 hardware configuration.
Nonrefresh segments differ in that they are drawn only
once, and not on each successive loop iteration. Normally
such segments will be drawn in storage mode, but this does
not have to be true. The primitive attribute REFRESH
determines the mode the Tektronix 4014 uses when generating
characters and vectors; therefore it is possible to draw non-
refreshed information that immediately disappears and to
draw storage-mode information that is continually refreshed
(not recommended). The general assumption, however, is that
refreshed segments will contain refresh commands and non-
refresh segments will contain storage commands.
Selective erase is implemented somewhat differently for
each type of segment. Refreshed segments merely have their
display flag turned off. Nonrefresh (storage) segments that are
erased cause the entire display to be erased, and the display
Hag for that segment is turned off; all other segments are
f lagged as not having been drawn. The result is that everything
but the erased segment is redrawn on the next pass of the
main loop. The redraw time is very short; the only objection
being the screen erase flash that precedes it. A typical mesh
plot containing about 1500 14-inch vectors takes about one
second to redraw.
Host Software
A package of Fortran interface subroutines on our PRIME-
300 minicomputer allows a user’s application program to
generate commands for the GRAF80 system. Access is allowed
to each segment-level and primitive-level command. The sub¬
routines generate the proper transmission formats, perform
data conversions where necessary, and send GRAF80
commands out the communications line to the microproces¬
sor. All coordinates used at this level are integers, which run
from 0-4095. This corresponds directly to Tektronix 4014
enhanced graphics screen coordinates, although any arbitrary
units could have been chosen. Appendix C contiiins documen¬
tation of these routines.
From the host computer’s viewpoint the system appears as
a virtual device, with built-in functions for picture segmenta¬
tion and refreshing. As such, it would be most useful when
interfaced to a higher-level graphics system. This higher-level
system could be an existing graphics package, modified to
accept GRAF80 as another device type and to include segment
manipulation features, or it could be a new system built on
top of GRAF80. In the latter case, an implementation of the
SIGGRAPH-ACM CORE system would be facilitated since
GRAF80 has several of the CORE functions already available.
Our 8080 microprocessor is only lightly loaded with the
current GRAF80 software (except when refreshing). Thus we
believe that much of the CORE system could be handled by
the microprocessor with additional software. Currently we
have designed, but not yet implemented on our microproces¬
sor, the image transformation features of the CORE system
and most of the input functions. We chose these functions for
microprocessor implementation since they can provide fast
interactive feedback to the user when placed on a processor
with a high-speed connection to the display device. Also, they
involve only fixed point coordinates. Today’s microprocessors
handle floating point computations only slowly in software.
We have left the transformations from floating point (world
coordinates) to fixed point (normalized device coordinates)
to our minicomputer which has floating point instructions.
As mentioned above, the limiting refreshing rate for
GRAF80 could be improved through revision of the data
structures. The graphics task could be modified to store
Tektronix 4014 code in a separate buffer, rather than display
it directly. A third refresh task would then display this buffer,
with no interpretive overhead. A small test program on our
microprocessor that used this technique was able to refresh
approximately 140 inches of vectors, about twice as much as
GRAF80 can currently refresh. However, our experience
so far has been that the segmenting features (which provide
selective erase) are more valuable for most users than the
refresh capability.
The handful of users with engineering applications who
have been exposed to GRAF80 have generally been quite
pleased with its capabilities. This is in part due to their
previous use of an overloaded mainframe (a not uncommon
occurrence) with a slow (300 to 2400 baud) data rate line to
their terminal. These conditions favor our use of local
intelligence and sending only changes in images instead of
sending the entire image each time a small change is made.
REFERENCES
1. Computer Graphics (11,3) Fall 1977.
2. A Guide to PL/M Programming, Intel Corp., Santa Clara,
California, 1973.
Page 40
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
81
AN ADDITION TO 8080 PILOT
I have added a “pause” command to my implementation
of the pilot interpreter (see DDJ #13 and #14). The com¬
mand “PAUSE:” delays approximately 1 second before the
program execution continues. “PAUSE:N” delays N seconds,
and N may be a number or numeric variable (similar to the
INMAX: command.
What makes the command useful is that the delay is inter¬
rupted by the pressing of any key and the program then
continues with the Y/N switch set for “N” and a new variable
“[” (shift-K) set to the number of seconds that expired before
the key was pressed. If the delay is not interrupted however,
the Y/N switch is set to “Y”.
Sincerely, 920 N. Washington St.
Robert Wilcox Owosso, MI 48867
AN EXAMPLE WILL SHOW HOW THE COMMAND CAN BE USED:
R! EXAMPLE OF A PILOT PROGRAM USING THE ’PAUSE:' COMMAND
♦BEGIN
T: WHAT IS YOUR NAME?
T:YOU HAVE 5 SECONDS TO ANSWER.
PAUSE: 5
JY:*T00SL0W
A:*N
T:YOU ANSWERED "SN" AFTER A #C SECOND DELAY.
J:*A$K
♦TOO SLOW
T:YOUR 5 SECONDS ARE UP!
♦ASK T:WANT TO TRY AGAIN?
A:
M:Y
JY:BEGIN
E:
CALL NMCTL
CPI CB
JZ PZl
ANA A
JNZ DELAY
PZl: M VI E# 1
DELAY! XRA A
STA YNSW ;SET FOR 'N'-NOT TIMED OUT
MOV D#A
MOV A# E
ADD A
MOV E# A
DELA1 ! LXI 3,2
DELA2t DCR C
JNZ DEL A 2'
DCR B
JNZ DEL AS:
INR D
CALL C0NSC.K ; SEE IF A KEY WAS PRESSED
JNZ STOP
DCR E
JNZ DELA1
ORA H
STA YNSW ; 'Y'-TIMED OUT
RET
#
;SET VARIABLE 'C' FOR NUMBER OF SECONDS BEFORE
;A KEY WAS PRESSED.
;
STOP:
MOV
RAR
A# D
MQV
D# A
LDVAR:
MVI
B# ’ C *
CALL
VARMCH
INX
H
MOV
RET
M# D
;
1CHECK FOR A KEY PRESSED
5
;INSERT HERE A ROUTINE WHICH TESTS TO SEE IF A KEY WAS
5PRESSED. IT SHOULD RETURN WITH A 0 IN THE ACCUMULATOR
UF NO KEY WAS PRESSED# OR A 1 IF A KEY WAS PRESSED..
;ALS0 THE ZERO FLAG SHOULD BE TESTED.
IFOR EXAMPLE!
THE ROUTINE TO BE ADDED TO PILOT IN ORDER TO
IMPLEMENT THE PAUSE! COMMAND FOLLOWS# ALONG WITH THE
MODIFICATIONS MADE TO THE "LETTER" AND "INITV"
ROUTINES THAT ARE NECESSARY IN ORDER TO ADD THE "C"
VARIABLE.
ALSO# THE COMMAND MUST BE ADDED TO "CTLST":
DB 'PAUSE '# 0DH
DW PAUSE
AND THE NVAR STORAGE AREA MUST BE CHANGED TO:
NVAR: DS 55
I HOPE THAT THIS ADDITION TO PILOT WILL BE USEFUL
AND I WOULD BE GLAD TO HEAR FROM ANYONE USING IT.
CONSCK:
IN
PORT ; CHECK STATUS PORT
AN I
l ;mask status bit
RET
#
LETTER
TESTS
WHETHER CHAR IS A-Z OR C
LETTER:
MOV
A# M
MOV
B# M
CPI
•A*
JM
NOTL
CPI
•Z’*2
JP
NOTL
XRA
A
RET
NOTL:
ORA
RET
H
;
;****PAUS E OPERATION ROUTINE****
#
.’PAUSE OPERATION - ’PAUSE:N’ DELAYS N SEC.
•IF ANY KEY IS PRESSED BEFORE THE DELAY TIME
JHAS EXPIRED. THE Y/N SWITCH IS SET TO 'N ' AND
ITHE VARIABLE ’C’ (SHIFT-K) IS SET TO THE
INUMBER OF SECONDS USED UP AND THE DELAY IS ENDED.
!
UF THE DELAY EXPIRES BEFORE A KEY IS PRESSED.
JTHE Y/N SWITCH IS SET TO *Y'. AND ’t • IS LEFT - a.
PAUSE: MVI D. 0
CALL LDVAR J SET VARIABLE ’t’ TO 0
#
; INITIALIZE NUMERIC VARIABLES A-Z AND C TO ZERO.
i
INITV: LXI H# N VAR
Number 42
82
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 41
A BUG IN SAM76 s CP/M
CORRECTION
Dear Suzanne:
Several months ago I submitted a text written in the
SAM 76 language to Claude Kagen at SAM76 inc. It emulated
the integer multiplication function available in the language
but did floating point multiplication.
Liter while attempting to impress a friend a bug in the
text became evident. The text failed in certiiin cases when
the number base of the interpreter was larger than ten.
Not realizing it might be used by SAM76 inc. I did not
bother to inform them of the problem.
A while ago I received the latest version of SAM76 which
is configured for CP/M. Included on the diskette were several
files with example texts in them. One of the files is the float¬
ing point multiplication text that is in error.
I would be very pleased if you would publish a correction
to this Text as it has been distributed for several months in
this form.
Thanks, 92 Granville Cres.
C.R. Jamieson Sherwood Park
Alberta, Canada
This is the original Text—
< mult >
Zdtrnl fZtsfC13//'
ZdtFn2FZrsFC23//'
8ptrnlr./8ptrn2r./'
Xdt m3 f 0123456789ABCDEF/' ,
Xdt f n3 fX fdc f n3 fX anb///'
XdtFn4F%muF%rsFZnl//FXrsFXn2 //F!XttfC33////'
ZdtFn5F%rsFXn4///'
Xdt f n5 fX hc fZ fts f n5 fX n3////'
XdtFn3FXadFXhcFXfeFnl//FXhCFXfeFn2////'
Xdt f n4 f Xis fX n5/F Xn3/ ? !Xn4// f !X psf-X n3 /f0fX n4/////'
XfdcFn4FXsUF Xn5/F Xn3///.Xfe f n4/'
XetFnlFn2Fn3Fn4Fn5/
Correct version —
< MUILT >
XdtFlFXrsFC13//XdtF2FXrsFC23//'
8 P t F 1 F ./*PtF2F ./'
Xdt f 3 f 0123456789ABCDEF/'
ZdtF 3FZfdCF3FXanb///'
XdtF 4 fXifiufXts f X1//f XtsfX2// f !Xrr f [33////'
Xdt F 5 F Xrs F Z4///Zdt f 6 fX anb//Zcnb f10/'
Xdt f 5 f Xhc f Xfts f 5 f X3////'
Xfdc f 4 f Xsu f Xhc f X4//f X5///'
XdtF3FXsdFXhCFXfeF1 //f Xhc f Xfe f2////'
XdtF4FXidFX5/FX3/F!X4 //f!Xpsf-X3/f0fX4/////'
Xfdc f4fXsufX5/f X3/// . Xfe f 4/Xcnb f X6//'
XetFlF2F3F4F5F6/
Examples of use
XhULT f 5 .f -6 . /=-30 .
XMULTf.007f7./=.049
XMULTFStrind -.007r7./=Strind -
XMULTf
123456789.123456789f987654321.987654321/=
121932631356500531.347203169112635269
Xdt f SQRf!XMULT f * f *///=
Xpt f !5QR f #/=
ZSQR f 2453.567/=6019991.023489
Xcnb»16/=
XSQR »2453.567/=5278B70.A9CF71
Dear DDJ:
Jim Warner of the University of California, Santa Cruz
was kind enough to inform me of an error in the UCSD
Pascal to CP/M transfer program which was published in DDJ
#37. The error occurs infrequently when a DLE-space code
crosses a 512 byte block boundary.
The enclosed partial listing replaces the original code from
30F hex to 3AD hex (with 16 bytes left over).
Sincerely, 9001 Laurel Grove Dr.
Ronald G. Parsons Austin, TX 78758
This was rewritten by J. Warner, UC Santa Cruz.
The GETBYT routine is a new single place to get
characters from the Pascal read buffer.
030F -
RB
EQU
$
030F 3AC704
LDA
TXTFL0
0312 PE02
CPI
2
0314 C25103
JNZ
N0T$TXT
0317 3ACB04
RBCKLP
LDA
NLP
031A B7
ORA
A
031B CA2503
JZ
RBCKTB
031E AF
XRA
A
031P 32CB04
STA
NLP
0322 3E0A
MVI
A ,LF
0324 C9
RET
0325 3ACC04
RBCKTB
LDA
NTB
0328 B7
ORA
A
0329 CA3303
JZ
RBPB
032C 3D
DCR
A
032D 32CC04
STA
NTB
0330 3E20
MVI
A, 1 1
0332 C9
RET
0333 CD5503
RBFB
CALL
GETBYT
0336 B7
ORA
A
0337 CA3303
JZ
RBPB
033A FE0D
CPI
CR
033C C24303
JNZ
CKDLE
033F 32CB04
STA
NLF
0342 C9
RET
0343 FE10
CKDLE
CPI
DLE
0345 CO
RNZ
0346 CD5503
CALL
GETBYT
0349 D620
SUI
32
034B 32CC04
STA
NTB
034E C32503
JMP
RBCKTB
0351 CD5503
NOT$TXT
CALL
GETBYT
0354 C9
RET
jread byte
;.TEXT?
jneed LP?
;need tab?
jread byte from buffer
jbypass O’s at end of 1024 byte
Page
jNeed Line Peed
jget the space code
jset indentation
; Oet the next character from the Pascal file.
; Read disk if necessary.
0355 -
0ETBYT EQU
0355 2ACD09
LHLD
0358 110012
LX I
035B CDB902
CALL
035E CC6703
CZ
0361 7E
MOV
0362 23
INX
0363 22CD09
SHLD
0366 C9
RET
$
BUFADD
D,BLKBUF+512
EQUAL
RBLK ;return with HL
A ,M
H
BUPADD
BLKBUP
0367 - RBLK
0367 2ACF04
036A EB
036B 2AD104
036E CDB902
0371 CA9803
0374 0E01
0376 CD1BBA
0379 110010
0370 CD8502
037F 118010
0382 CD8502
0385 110011
0388 CD8502
038B 118011
038E CD8502
0391 210010
0394 22CD04
0397 C9
0398 21CA04 SETEOF
039B 3601
039D C9
EQU S
LHLD LSN
XCH0
LHLD LSTLSN
CALL EQUAL
JZ SETEOF
MVI C,1
CALL SELDSK
LX I D,BLKBUP
CALL RDSEC
LXI D.BLKBUP+80H
CALL RDSEC
LXI D,BLKBUF+100H
CALL RDSEC
LXI D,BLKBUF+l80H
CALL RDSEC
LXI H,BLKBUP
SHLD BUPADD
RET
LXI H,E0FFLAG
MVI M,1
RET
jread LSN block
jfound last sector
jselect B disk
jread four sectors
Page 42
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
83
THE SIMPLER PLEASURES
Dear DDJ,
You published a short article of mine in DDJ #34 entitled
“Increase Your Poly 88 Pleasure.” It described how to com¬
bine two or more BASIC programs. Since I wrote that article,
I have discovered a much simpler way of combining programs.
Enclosed are the newer instructions. I hope you can find the
space to print this new information.
Thank you, 4104 Montreal Ave.
David Larry Johnson Prince George, VA 23875
Combining Poly 88 A00 BASIC Programs
The key to combining A00 BASIC programs is in mani¬
pulating two “pointers.” At locations 205D-205E is a pointer
which points to the beginning of free memory space after the
end of BASIC. The pointer is in normal 8080 reversed byte
format. A second pointer at 48AA—48AB points at the next
available byte after the end of the current program in memory.
After a SCRatch these two pointers point at locations ad¬
jacent to each other. With this knowledge it is very simple
to combine programs by following these steps:
1. Using front panel mode examine 205D—205E and write
down the contents. This pointer value will be needed later.
(May be 49BO.)
2. LOAD the first program.
3. LIST the program to determine the line number of the last
line in the program. Write this down also.
4. Using front panel mode change the contents of 205D—
205E to the contents of 48AA--48AB minus one. What you
are doing here is moving the beginning-of-memory pointer
up next to the next-available-byte pointer. Now cold start
BASIC with a front panel jump to location 2000. Now your
first program is still in memory, but BASIC’s pointers are
positioned after it so as far as BASIC is concerned, it does
not exist.
5. Now LOAD the next program. RENumber it so its first
line number is greater than the last line number of the first
program (the number you wrote down in step 3).
6. Using front panel mode change the contents of 205D—
205E back to their initial values that you wrote down in step 1.
7. And finally, warm start BASIC by using a front panel
jump to location 2003.
Now if you type LIST you will see that both programs are
there. You can now SAVE the combined programs or RUN
them or do anything else with them that you could do with
either one by itself. To RUN the second program you must
type RUN XXXX where XXXX is the first line number of the
second program. You can add a short routine at the beginning
of the first program which asks which program to run and
then jumps to the correct one.
There are some potential problem areas associated with
joining programs this way:
1. Unless you type RUN to execute each program each time,
then variables commmon to both programs may not get ini¬
tialized properly.
2. If you have DATA statements in both programs, a RE¬
STORE will always restore to the first DATA statement in the
first program. Use RESTORE referenced to a specific line
number to avoid this problem.
3. If you have defined functions with the same name in both
programs, you will have to change all the names of the func¬
tion in one or the other of the two programs.
4. If there is not STOP at the end of the first program, you
may “fall through” into the second program when you do not
want to.
This technique for joining programs is quicker to do than
to read these instructions. It works very well too. It is not
necessary to stop at joining only two programs. You can
continue adding programs until you run out of memory or
out of programs. I have combined as many as ten or twelve
short demonstration programs into one SAVE and LOAD
unit on tape.
ANOTHER PHONE DIALER
Dear Editor:
I used the algorithm from Cash Olsen’s “Fast Repertory
Telephone Dialer Program” (DDJ #38) to develop an auto¬
matic phone dialer for my PET.
I used the Microtronics M65 HAM Interface. The relay is
placed in series with the green wire to the phone and works
fine. I used a phone plug jack which closes the circuit for the
green wire for normal phone operation when the computer is
unplugged.
The program is documented with REM statements and is
self explanatory in conjunction with Olsens article.
Thanks 8285 Royall Oaks Dr.
Gary Lindensclimitt Roseville CA 95678
REFIDV.
1 REM LINDV/EDIM *DIALER* DR DOBBS SEP79
2 REM DRIVE RELAY FROM USER PORT PAO
3 P0KE59459.255
10 PRINT'CHMSi)"
11 PRINT PRINTPRINT“WOULD YOU LIKE ME TO CALL SOMEONE?" GOTO 21
20 PRINT PRINT : PRINT"B0 YOU WANT ME TO F'HONE SOMEONE ELSE ?”
21 GET 0SIF G$- ’" THEN 21
22 IF G*="Y" THEN PRINT".1!I«BWWH0 SHOULD I CALL"; -GOTO 2000
23 PRINT"."WnttWHMiSTHANK YOU.B":STOP
30 D-l : IFZ-1THENGOSUB110
35 IFA=1THEN40O
40 IFA>=999THEN60
50 F=A E= 100 GOSUB300
60 IFP>999THEN20
65 PRINT"
70 F=P E= 100 GOSIJE300
75 PRINT"
80 IFL399S9THEN20
85 F=L ; E=1000 GOSUB300
90 GOTO 2050
100 IFD=0THEND=10
110 F0RN=1TOD
120 REM OPEN RELAV 33MS
121 P0KE59459,255:P0KE594?1,1
125 T=1:C=TI
126 B=TI
128 IFB>=C+<T*2 'THEN132
130 GOTO126
132 REM PRINTCB-O/60
134 REM CLOSE RELAY 16MS
135 T=1 : C=TI P0KE59471,0
137 B=T1
138 IFBJ=C+*T*l > THEM140
139 GOTO137
140 REM PRINT'. B-CV60
141 MEKTN
142 T=1 C=TI
143 B-TI
144 IFB3=C+'T*12:'THEH146
145 GOTO 143
146 REM PRINTCB-O/60
150 RETURN
300 D=INTtF/E> F=F-CD*E)
305 PRINTO.
310 00SUB100
320 1F£=1THENRETURN
330 L>E/10 GOTO3O0
Number 42
84
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Bex E, Menlo Park, CA 94025
Page 43
400 D=1 : PRINT" 1 ";
41£l G0SUB1 10
4£Ci GOT060
500 END
99C REM**IMSERT DAT* STMTS HERE**
995 REM**"NAME",AREA CODE,PREFIX,LAST
996 REM FOUR DIGITS**
997 REM**FOR LOCAL CALLS USE 1000 **
1000 DATA“WORK",1,916,643.4601
1O10 DATA"HOME",1,916.791,4298
1020 DATA“MOM",0,1000,725,5966
1OS0 DATA"TIME”,0,1000,783,1600
1040 DATA"JIM ELROD",0,1,988,4848
1O50 DATA"EOB 2INKV",1,1000,421,1350
1070 DATA"JOE SUDDUTH",1,209,745,4331
1080 DATA"JACK EBIN",0,1000,791,7618
1090 DATA"DALLAS PARCHER",1,1000,486,0868
1999 DATA "END",0,0,0,0
2000 RESTORE:INPUTN*
2001 PRINT'.-WiWW
2002 PRINT"DIAL I NO "S'WB";“ NOW"
2003 PRINT PRINT
2018 RLADMt,Z,A,P,L
2015 II' M*0"END"THEN 2020
2017 PRINT"I M SORRY BUT I DO NOT KNOW THAT NUMBER"
2018 PRINT-WIDIS THERE SOMEONE ELSE YOU WOULD LIKE ME TO CALL 9 " GOTO 21
2020 IFN*OM*THEN2010
2025 F'RINT"afiREA CODE PREFIX NUMBER"
2030 PRINT •'PRINTA, P, L :FRINT
2040 RESTORE
2045 GOTO 30
2050 PRINT PRINT"WWHWaWAIT FOR RING" PRINT
2051 I *'jR I=1 TO10000 : NEXT
2052 PRINT PRINT"WUDO YOU WANT ME TO DIAL THE SAME NUMBER AGAIN?";
2055 GET C* IF C*=“" THEN 2055
2060 I!' C*0*V" THEN 20
2061 REM HANO UP FOR 3 SEC * DIAL AGAIN
2062 PRINT"OK" : X=1
2065 P0KE59471,X
2070 T=3 C=TI
2072 B=TI
2074 1FB>=C+<T*60)THEN2080
2076 G0T02072
2079 PRINT(B-O/60
2080 IFX=0THEN2GO1
208,2 X=0 GOTO2065
2095 OOTO20O1
READY.
ABOUT THE PERSONAL COMPUTING SOCIETY
To DDJ Readers:
I am frequently asked why, in regard to why the Personal
Computing Society is trying so hard to become a vital service
force for the personal computer user. Hobbyist groups dot the
country, courteously exchanging newsletters. Professional
groups, such as those under ACM, span the country, addressing
issues of importance, such as educational and handicapped
applications, standards development, data security and the
like. Is not, then, PCS redundant?
There are two major differences between the Personal
Computing Society and those referenced above:
(1) For those already involved with computers, there is a
substantial cost efficiency. A nominal dues fee gives you access
to one central source of information, and one centralized
agency coordinating your opinion with those who share it
across the country.
Professional organizations charge expensive fees, since these
moneys, often reimbursed by members’ employers, must
support massive professional staffs and housing facilities.
PCS requests a fee of $10 annually for individuals, but
clubs can bring their entire membership into our fold for a flat
$25. Projects currently underway include a study of legal and
taxation considerations for hobbyist organizations, a network
capability stringing together the bulletin board facilities
already utilized by individuals and clubs across the country,
and a newsletter. These are projects of interest to hobbyists;
there are others for educators, consumers, varying special
interest groups.
(2) The PCS addresses the problems of the lay public, as
well as the computer expert. No hobbyist or professional
organization reaches the potential first-time user to educate
him so that he can purchase wisely. Those of you who al¬
ready use computers are gravely affected by the ignorance of
the public. Unless the lay person is aided with purchase
guidelines, this vast market remains untapped as a source of
influence on manufacturers. The vendors then remain free to
produce without guidelines of quality assurance, and without
listening to the needs of the user.
Following purchase, the novice computer user becomes one
of your number. He will require the same supportive informa¬
tion exchange hobbyists and professionals enjoy, but will not
know this exchange exists, let alone where to find it. Allowed
to enter the information network, the novice becomes an
expert, adding his talent to the pool upon which computer
users draw for assistance. Thus, the computer expert needs the
support of this uninitiated public, and should reach out to it.
All that we do is accomplished by volunteers. We wish to
keep personal computing within the personal control of the
individual user, so that he can determine the quality of his
equipment, while increasing his knowledge in its use. We aim
to accomplish this goal at a minimal cost, by circumventing
bureaucratic overhead and appealing to members to help each
other.
The most important contribution you can make is your
ideas. When you join, we become your group. It is up to
you to tell us what you want accomplished. It is up to us,
the collective, to make it happen.
For further information, write Abby Gelles, Executive
Director, Personal Computing Society, Inc., Box 147, Village
Station, New York, New York 10014. If you wish to join at
this time, enclose a $10 (individual) or $25 (organizations)
check payable to Personal Computing Society, Inc. Thank
you.
Abby Gelles Personal Computer Society
The Executive 185 W. Houston St.
NY NY 10014
Dear Dr. Dobb’s,
Amberse M. Banks article, page 43 of DDJ #39, was a big
help to me for Ver 4 Northstar DOS.
As I also use the XEK Assembler from the Byte Shop of
Westminster that requires Ver 2 DOS, I needed the two
column approach for Ver 2 as well.
Attached is a copy of the changes needed for Version 2.
Sincerely,
Don Dodge
5291 Kenilworth Dr.
Huntington Beach CA, 92649
0000
0000
0000
0000
0000
0000
29E0 0E 0C
29E2 CD 02 2 7
29E5 0D
29E6 C 2 E2 29
29E9 C 9
2 9 EA
2 9 EA
2 9 EA
29 EA
2 9 EA
0010 ; V ER S10 N 2 NORTHSTAR PATCHES TO GIVE TWO COLUMN OUTPUT
0020 ; B Y DELETING CR LF CALL AND SUBSTITUTING A SPACING ROUTINE
0030 ;T0 EVEN OUT THE COLUMNS. ROUTINE FOR VER 4 AND VER 5
0040 ; PUB LI SHED IN DR. DOBBS, NUMBER 39, OCTOBER 1 979,
0050 ; V0 LUM E 4, ISSUE 9. AUTHOR AMBERSE M. BANKS.
0060 ORC 29E0H
0070 MV I C , 12 ; ADD 12 SPACES FOR COLUMNS
0080 SPACE CALL 2 702H ;CA LL SPACE ROUTINE
0090 DC R C
0100 JNZ SPACE
0110 R ET
0120 ;
0130 ; A LSO CHANCE CALL AT 2707 FROM CD 07 2 7 TO CD E0 29
0140 ;B Y DON DODGE
0150 ; 5291 KENILWORTH DR.
0160 ; HUNTINGTON BEACH CA, 92649
SYMBOL TALLE
SPACE 29E2
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94305
Number 42
85
Dr. Dobbs Journals
COMPUTER
(Calisthenics Orthodontia
Running Light Without Overbyte
Number 43 March 1980 Volume 5, Issue 3
A REFERENCE JOURNAL FOR USERS OF HOME COMPUTERS
Mathematical Typography 5
Donald E. Knuth
TI9900: Fully Reentrant Formatter Operating Under TIPMX, Part 2 26
Norman V. Walters
SYMBOL: Generating Symbol Table Alpha Listing on the H8 21
William W. Moss
A Hex Keyboard with Applications for the 1802 ELF 40
Martin Bronstein
Can You Afford to Retire? 39
David E. Raeside
87
Mathematical
Typography
BY DONALD E.KNUTH
Computer Science Department
Stanford University
Stanford, California 94305
©1979 by the American Mathematical Society
ABSTRACT.
Mathematics books and journals do not look
as beautiful as they used to. It is not that their
mathematical content is unsatisfactory, rather
that the old and well-developed traditions of
typesetting have become too expensive. For¬
tunately, it now appears that mathematics itself
can be used to solve this problem.
A first step in the solution is to devise a
method for unambiguously specifying math¬
ematical manuscripts in such a way that they
can easily be manipulated by machines. Such
languages, when properly designed, can be
learned quickly by authors and their typists,
yet manuscripts in this form will lead directly
to high quality plates for the printer with little
or no human intervention.
A second step in the solution makes use of
classical mathematics to design the shapes of
the letters and symbols themselves. It is
possible to give a rigorous definition of the
exact shape of the letter “a”, for example, in
Reprinted from Donald E. Knuth,
Mathematical Typography, ” Bulletin
(New Series) of the AMS, volume 1,
number 2, pp. 337-372, by permission of
the American Mathematical Society. This
article is theJosiah Willard Gibbs Lecture
given by Mr. Knuth in February, 1978.
such a way that infinitely many styles (bold,
extended, sans-serif, italic, etc.) are obtained
from a single definition by changing only a few
parameters. When the same is done for the
other letters and symbols, we obtain a math¬
ematical definition of type fonts, a definition
that can be used on all machines both now and
in the future. The main significance of this
approach is that new symbols can readily be
added in such a way that they are automatically
consistent with the old ones.
Of course it is necessary that the math¬
ematically-defined letters be beautiful
according to traditional notions of aesthetics.
Given a sequence of points in the plane, what is
the most pleasing curve that connects them?
This question leads to interesting mathematics,
and one solution based on a novel family of
spline curves has produced excellent fonts of
type in the author’s preliminary experiments.
We may conclude that a mathematical ap¬
proach to the design of alphabets does not elim¬
inate the artists who have been doing the job
for so many years; on the contrary, it gives
them an exciting new medium to work with.
INTRODUCTION.
I will be speaking today about work in
progress, instead of completed research; this
was not my original intention when I chose the
subject of my lecture, but the fact is I couldn’t
get my computer programs working in time.
Fortunately, it is just as well that I don’t have a
finished product to describe to you today,
because research in mathematics is generally
much more interesting while you’re doing it
than after it’s all done. I will try therefore to
convey in this lecture why I am so excited
about the project I am currently working on.
My talk will be in two parts, based on two
different meanings of its title. First I will speak
about mathematical typography in the sense of
typography as the servant of mathematics: the
goal here is to communicate mathematics ef¬
fectively by making it possible to publish
mathematical papers and books of high qual¬
ity, without excessive cost. Then I will speak
about mathematical typography in the sense
of mathematics as the servant of typography:
in this case we will see that mathematical ideas
can make advances in the art of printing.
PRELIMINARY EXAMPLES.
To set the stage for this discussion I would
like to show you some examples by which you
can “educate your eyes” to see mathematics as
Number 43
88
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 5
a piinter might see it. These examples are taken
from the Transactions of the American Math¬
ematical Society, which began publication in
1900 ; by now over 230 volumes have been pub¬
lished. I took these volumes from the library
shelves and divided them into equivalence
classes based on what I could perceive to be
different styles of printing: two volumes were
placed into the same class if and only if they
appeared to be printed in the same style. It
turns out that twelve different styles can be
distinguished, and it will be helpful for us to
look at them briefly.
The first example (Fig. la) comes from page
2 of Transactions volume 1; I have shown only
a small part of the page in order to encourage
you to look at the individual letters and their
positions rather than to read the mathematics.
This typeface has an old-fashioned appearance,
primarily because the upper case letters and the
taller lower case ones like ‘h’ and ‘k’ are nearly
twice as tall as the other lower case letters, and
this is rarely seen nowadays. Notice the style of
the italic letter ‘x’, the two strokes having a
common segment in the middle. The subscripts
and superscripts are set in rather small type.
This style was used in volumes 1 to 12 of
the Transactions, and also in the first 21 pages
of volume 13. Then page 22 of volume 13
introduced a more modern typeface (Fig. lb).
In this example the subscript is still in a very
small font, and unfortunately the Greek Ct here
is almost indisinguishable from an italic ‘a’.
Notice also that the printer has inserted more
space before and after parentheses than we are
now accustomed to. During the next few years
the spacing within formulas evolved gradually
but the typefaces remained essentially the same
up through volume 24: with one exception.
The exception was volume 23 in 1922 (Fig.
lc), which in my opinion has the most pleasing
appearance of all the Transactions volumes.
This modem typeface is less condensed, making
it more pleasant to read. The italic letters have
changed in style too, not quite so happily -
note the ‘x’, for example, which is not as nice
as before — but by and large one has a favorable
impression when paging through this volume.
Such quality was not without its cost, however;
according to a contemporary report in the AMS
Bulletin [45, p. 100], the Transactions came
out 18 months late at the time! Perhaps this is
why the Society decided to seek yet another
printer.
In order to appreciate the next change, let’s
look quickly at two excerpts from the Bulletin
relating to the very first Gibbs lecture (Fig. 2).
The preliminary announcement in 1923 ap¬
peared in the modem typeface used during that
year, but the letter shapes in the report of the
first lecture in 1924 were very cramped and
stilted. The upper case letters in the title are
about the same, but the lower case letters in the
text are completely different.
This same style appeared in volume 25 of
the Transactions (Fig. Id), which incidentally
was set in Germany in order to reduce the cost
of printing. Note that the boldface letters and
the italic letters in this example are actually
Paga 6
«
(a)
(c)
(e)
( 8 )
(i)
(k)
X = ± >/\S =■ db V'*(aa'a")(«aa"j
there correspond two quadric forms each contain
rameters. So much Hilbert states. In order fc|
as known systems it will l>e convenient to use
mental cubic, due to Hesse.*
Referred to an inflexional triangle, the equati
(3) o’ = a] + ar] + a.'] + 6mx,x{
All conic polars accordingly have the form :
(4) « e; = (y,®; + yy.) + yy\) + 2 m{ypp.
I call this ineffective part of x, “ innocuous"
validate the fundamental proposition
(!(*i) AJ{x,)) = (x, *
which was proved above (P. 4) for effective val
ineffective part of x t is innocuous is clear: it,
that the variation of x t does not take place in it
D. 3. But this consideration leads to the defiri
cf x. By this I mean the collection of values wlj
(5)
* 2 , •••, x m :y it y*,
in v/hich the <p m are polynomials in ijx, y 5 , • • • , t
has been considered recently by W. D. Mj*
usual algebraic elimination theory to the p<
*(*t» * 2 » •••» x m :y m ) would be found fo
*(0.0, • • •, 0 : y m ) would be, say, of degree p.
theorem to (r it x 2 , •••,**: y m ), therefore,
degree p would appear. This is not in general t
is sought in this paper, as may readily be sho
The polynomials may have roots for which
of systems of division algebras. The next syst
of order over F with the basal units i*j h k* (
with an irreducible equation of degree pq, three
rational functions Q{i) and \p{i) with coefficie
iterative 0*(») of ff(i) is i, and likewise \p p (t)
by
«*[*'(*•)]-#'[«*(.•)] (* = 0,1, • - ■ , q-V
The complete multiplication table of the un|
associative law from
k p = y ,
six planes yif-yt = 0, each counted three tim
type j, y, — y, y, =- 0, each counted twice.
We have seen that any point on the line y, -f
image in (X) the whole line A, + X, = 0, A',
in ( y ) meets the line in one point, its image s', coj
the system s» has also the three lines of this typ
12. Algebraic procedure. The plane cot
and the vertex (1, 0, 0, 0) has the equation
I'.u x. + 7 'is x, -j-p.j x t
Since (y) and (y) both satisfy this equation wo
z=e“z° = (*"*?.0 SSg 2a,
C" is called a Reinhardt circular set if along w
I e E also the set
{ Z II Z »M Z !I> *=1.2 .n)
bounded closed subset of C", unisolvent with respect 1
The function b(z) being defined and lower semic
h (,> = {h\ r) . h™}, v 0 =
(b)
(d)
(f:
0 - r»x(2> i£Ii ) - (XV.adxr, = T.
i-1
This element is of lower length. It follows there
i = 1, Hence, (a) yields that r; =- A;/*, Aj
Now r k ^ 0, by the minimality of k, and y^A,<l
which we deduce that y.Aj an =* 0. But the a, a
which is impossible since in particular A* = 1.
Theorem 7. Let R be a dense ring of linear t.
F be a maximal commutative subfield D. If Rp
tion of finite rank over F, then R contains als*
The algebra P is nearly simple if and only if thi
(a) N is spanned by a, • • • , a n ~ k ~ *, b , • • s
*• / - 1. • *. *•
(b) Either n - k = char F u/ith k even or n
Proof. By Theorem 5.5, there are element:
fl » * ' ’ • a ' Furthermore, ab .
for all i, / where each a., X.. is in F. From t!
space of the space spanned by a n ~ k ~ 1 , ..,
Assume P is nearly simple. Then there is
show that each is in Al. To do this, it is nec
>f Q , i.e.
*) = 0 for every x G A for which x(Q) = 0}.
or m A is equivalent to the one induced by the
(|x(z)|: xE:A. M<1 and x(w) = 0}.
present the open unit disk in the complex plane, C,
t polydisk in n-dimensional complex space C n . T n
ioundary of D n t i.e.
The set N x is nowhere dense in Z x and thus N=»p(i
For each £ e Y—N we must prove that/ c satisfiij
be the unique projection in {P d \ de D) such that
the algebra (EjJE) P 0 is finite and homogeneoil
onal abelian projections E u E it ..., E n such that)
(l £j, k£n) be partial isometric operators in (EsJ
(1) U lk U lm =*h mt U lk , where S is the Kronecker dc|
(2) and
(3) U„=E h
for all 1 £j,kj,m£n. For each A in (Es/E)-P 0t t’
in & x Po such that
:tions in GL(IK) and h afi , a, P G / as coordinate
ined by the respective bases chosen above. If a,
jnction of A* is the minor of |g^| determined by
columns /J(l),..., p(j>). The coordinate ring of
a p together with l/det|/i a ^|, while that of GL(W0
Dgether with l/det|g^|. The coordinate functions
so to show A' is a morphism it suffices to show
nial in and l/det|gj. For this, the following
haracter of GL( W) is an integral power of the
:onverges pathwise to and uniformly for t G
: for which X t is the (last) minimum of y\ let }j\|
dues of and T, x the inteijump times for Y
st an i such that )■* = T* = oo. Notice that Yq
id that as e -* 0, Yq converges to / x = inf s X*. Le|
ts of (—oo, oo). Then, for example, if / > 1
e B, r e \ t - y 0 x e C, r e \ k e D,N>Q>i)
e a, T,\ e b, - y/ e c,t +k sd.n>q
(©
(J)
(/)
Figure 1. A sequence of typographical styles in the AMS Transactions:
(a) vol 1 (1900), p. 2; (b) vol 13 (1912), p. 135; (c) vol 23 (1922), p. 216;
(d) vol 25 (1923), p. 10; (e) vol 28 (1926), p. 207; (f) vol )05 (1962), p. 340;
(g) vol 114 (1965), p. 216; (h) vol 125 (1966), p. 38; (i) vol 169 (1972), p. 232;
(j) vc! 179 (1973), p. 314; (k) vol 199 (1974), p. 370; (I) vol 225 (1977), p. 372.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
89
quite beautiful - and we’re back to the good
old style of ‘x’ again — so the mathematical
formulas looked great while the accompany¬
ing text was crowded. Fortunately only three
volumes were published in this style.
A new era for the Transactions began in
1926, when its printing was taken over by the
Collegiate Press in Menasha, Wisconsin. Vol¬
umes 28 through 104 were all done in the same
style, covering 36 years from 1926 to 1961,
inclusive, and this style (Fig. le) was used also
in the American Mathematical Monthly. In
general the modem typefaces were quite satis¬
factory, but there was also a curious anomaly:
Italic letters used in subscripts and superscripts
of mathematical formulas were in a different
style from those used on the main line! For
example, notice the two k’s in the first dis¬
played formula of Fig. le: the larger one has a
loop, so it is topologically different from the
smaller one. Similarly you can see that the p in
k^ is quite different from the p in p^. There are
no x’s in this example, but if you look at other
pages you will find that the style of x that I like
best appears only in subscripts and superscripts.
I can’t understand why this discrepancy was
allowed to persist for so many years.
Another period of typographic turmoil for
the Transactions began with volume 105 in
(1962). This volume, which was typeset in
Israel, introduced a switch to the Times Roman
typeface (Fig. 10; an easy way to recognize the
difference quickly is to look at the shading on
the letter o,since it now is somewhat slanted; in
the previously used fonts this letter always was
more symmetrical, as if it were drawn with a
pen held horizontally, but in Times Roman it
clearly has an oblique stress as if it were drawn
by a right-handed penman. Note that the three
k’s are topologically the same in the displayed
equation here; but for some reason the two
subscripts k’s are of different sizes. Many of the
Times Italic letters have a somewhat different
style than the readers of the Transactions had
been accustomed to, and I personally think that
this font tends to make formulas look more
crowded. Actually the changeover to Times
Roman and Times Italic wasn’t complete; the
italic letter g still had its familiar shape, perhaps
because the new shape looked too strange to
mathematicians.
Volumes 105 through 124 were all done in
this style, except for a brief interruption: In
volumes 114, 115, and 116 the shading on the
o’s was symmetrical and the k’s had loops
(Fig. lg). Another style was used for volumes
125-168 (Fig. lh): again Times Roman was the
rule, even in the g’s, except for subscripts and
superscripts which were in the style I prefer; for
example, compare the j’s and k’s. (These latter
volumes were typeset in Great Britain.)
A greatly increased volume of publication,
together with the rising salaries of skilled per-
sonel, was making it prohibitively expensive to
use traditional methods of typesetting, and the
Society eventually had to resort to a fancy
form of typewriter composition that could
simply be photographed for printing. This un-
TIIE JOSIAH WILLARD GIBBS LECTURESHIP
The Council of the Society has sanctioned the establishment
of an honorary lectureship to be known as the Josiah Willard
Gibbs Lectureship. The lectures arc to be of a popular nat arc
on topics in mathematics or its applications, and are to be
given by invitation under the auspices of the Society. They
will be held annually or at such intervals as the Council may
direct. It is expected that the first lecture will be delivered
in New York City during the winter of 1923-24, and a com¬
mittee has been authorized to inaugurate the lectures by
choosing the first speaker and making the necessary arrange¬
ments.
1L G. D. Richardson,
Secretary.
THE FIRST JOSIAH WILLARD GIBBS LECTURE
The first Josiah Willard Gibbs Lecture was delivered
under the auspices of this Society on February 29, 1924,
by Professor M. I. Pupin, of Columbia University, iu the
auditorium of the Engineering Societies' Building, New York
City. A large and distinguished nndience was present,
including, besides members of the Society, many physicists,
chemists, and engineers who had been invited to attend.
In introducing the speaker, President Vcblen spoke as
follows:
“In instituting the Willard Gibbs Lectures, the American
Mathematical Society has recognized the dual character of
mathematics. On the one hand, mathematics is ouc of the
essential emanations of the human spirit,—a thing to be
valued in and for itself, like ail or poetry. Gibbs made
Figure 2. A time of transition. (Excerpts from the AMS Bulletin 29 (1923), p. 385; 30 (1924),
p. 289.)
Formula
Type C
Type B
Type T
1
z
$fl$s2$t
1 over 2
1 \over 2
-&*
*gq"2
theta sup 2
\thetaT2
$rf(x’i)$t
sqrt{f(x sub i )}
\sqrt{f(xii)>
Figure 3. Three ways to describe a formula.
fortunate circumstance made volumes 169-198
of the Transactions look like Fig. li, except for
volumes 179, 185, 189, 192, 194, and 198
which were done in a far better (yet not wholly
satisfactory) style that can be distinguished
from Fig. If by the italic g’s. Fig. lj was
composed on a computer using a system de¬
veloped by Richard McQuillen; this was one of
the fruits of an AMS research project supported
by the National Science Foundation [2, 3,
4,5,6],
Computer typesetting of mathematics was
still somewhat premature at the time, however,
and another kind of “cold copy” made its ap¬
pearance in volumes 199 through 224 - an
“IBM Compositor” was used, except for vol¬
umes 208 and 211 which reverted to the Vari-
typer style of Fig. li. The new alphabet was
rather cramped in appearance, and some words
were even more crowded than the others (see
Fig. Ik). At this point I regretfully stopped sub¬
mitting papers to the American Math. Society,
since the finished product was just too painful
for me to look at. Similar fluctuations of typo¬
graphical quality have appeared recently in all
technical fields, especially in physics where the
situation has gotten even worse. (The history of
publication at the American Society of Civil
Engineers has been discussed in an interesting
and informative article by Paul A. Parisi [44].)
Fortunately things are now improving. Be¬
ginning with volume 225, which was published
last year, the Transactions now looks like Fig.
11; like Fig. lj, it is computer composed, and
the Times Roman typeface is now somev/hat
larger. I still don’t care for this particular style
of italic letters, and there are some bugs need¬
ing to be ironed out such as the overlap be¬
tween lines shown in this example; but it is
clear that the situation is getting better, and
perhaps some day we will once again be able to
approach the quality of volumes 23 and 24.
COMPUTER-ASSISTED COMPOSITION.
Perhaps the main reason that the situation is
improving is the fact that computers are able to
manipulate text and convert it into a form
suitable for printing. Experimental systems of
this kind have been in use since the early 1960’s
(cf. the book by Barnett [10]), and now they
are beginning to come of age. Within another
ten years, I expect that most office typewriters
will be replaced by television screens attached
to a keyboard and to a small computer. It will
be easy to make changes to a manuscript, to
replace all occurrences of one phrase by
another and so on, and to transmit the manu¬
script either to the television screen, or to a
printing device, or to another computer. Such
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Page 7
systems are already in use by most newspapers,
and new experimental systems for business
offices actually will display the text in a variety
of fonts [26]. It won’t be long before these
machines change the traditional methods of
manuscript preparation in universities and tech¬
nical laboratories.
Mathematical typesetting adds an extra level
of complication, of course. Printers refer to
mathematics as “penalty copy”, and one of
America’s foremost typographers T. L. De
Vinne wrote that “[even] under the most
favorable conditions algebra will be trouble¬
some.” [17, p. 171] The problem used to be
that the two-dimensional formulas required
complicated positioning of individual metal
pieces of type; but now this problem reduces
to a much simpler one, namely that two-di¬
mensional formulas need to be represented as a
one dimensional sequence of instructions for
transmission to the computer.
One-dimensional languages for mathemat¬
ical formulas are now familiar in programming
languages such as FORTRAN, but a somewhat
different approach is needed when all of the
complexities of typesetting are considered.
In order to show you the flavor of language for
mathematical typesetting, I will briefly describe
the three reasonably successful systems known
to me. The first, which I will call Type C, is
typical of the commercially available systems
now used to typeset mathematical journals such
as the Transactions ( cf. [12]). The second,
which 1 will call Type B, was developed at Bell
Telephone Laboratories and has been used to
prepare several books and articles including the
article that introduced the system [27]. The
third, which I will call Type T, is the one I am
presently developing as part of the system I call
TEX [29]. (This has no connection with a
similarly-named system recently announced by
Honeywell Information Systems. In my lan¬
guage, the T, E, and X are Greek letters and
TEX is pronounced “tech”, following the
Greek words for art and technology).
Fig. 3 shows how three simple formulas
would be expressed in these three languages.
The Type C language uses $f...$s...$t
for fractions, *g for “the next character is
Greek,” q for the Greek letter theta, ” for
superscripts, $r . . . $t for square roots and ’
for subscripts. The Type B language is more
mnemonic, using “over”, “theta”, “sup”,
“sqirt”, and “sub” together with braces for
grouping when necessary. The Type T language
is similar but it does not make use of “re¬
served words”; a special character \ is used
before any nonstandard text. This means that
spaces can be ignored, while they need to be
inserted in just the right places in the Type
B la nguage; for example, the space after the “i”
is important in the example shown, otherwise
f(xj) would become f(xj) according to the
Type B rules. Another reason for the \ delimi¬
ter in Type T is that it becomes unnecessary
to match each text item against a stored dic¬
tionary, and it is possible to use “sup” to mean
supcemum instead of superscript. The special
symbols \ { } t 4- in Type T can be changed
to any other characters if desired; although
these five symbols don’t appear on conven¬
tional typewriters, they are common on com¬
puter terminal keyboards.
Incidentally, computer typesetting brings us
some good news: It is now quite easy to re¬
present square roots in the traditional manner
with radical signs or vinculums, so we won’t
have to write x'' 2 when we don’t want to.
(Added in proof: I was pleased to find that this
announcement was greeted with an enthu¬
siastic round of applause when I delivered the
lecture).
None of these languages makes it possible
to read complex formulas as easily as in the
two-dimensional form, but experience shows
that it is not difficult for untrained personnel
to learn how to type them. According to
[12]. “Within a few hours (a few days at most)
a typist with no math or typesetting back¬
ground can be taught to input even the most
complex equations.” And the Type B authors
[27] report that “the learning time is short.
A few minutes gives the general flavor, and
typing a page or two of a paper generally
uncovers most of the misconceptions about
hew it works.” Thus it will be feasible for
both typists and mathematicians to prepare
papers in such a language, without investing a
great deal of effort in learning the system.
The only real difficulties arise when preparing
tables that involve tricky alignments.
Once such systems become widespread,
authors will be able to prepare their papers
and see exactly how they will look when
printed. Everyone who writes mathematical
papers knows that his intentions are often
misunderstood by the printer, and corrections
to the galley proofs have a nontrivial prob¬
ability of introducing further errors. Thus, in
the words of three early users of the Bell Lab’s
system, “The moral seems clear. If you let
others do your typesetting, then there will
be errors beyond your control; if you do your
own, then you have only yourself to blame.”
[1] Personally, I can’t adequately describe
hC'W wonderful it feels when I now make a
change to the manuscript of my book, as it
is stored in the Stanford computer, since I
know that the change is immediately in effect;
it never will go through any middlemen who
might misunderstand my intention.
Perhaps some day a typesetting language
will become standardized to the point where
papers can be submitted to the American
Mathematical Society from computer to com¬
puter via telephone lines. Galley proofs will
not be necessary, but referees and/or copy
editors could send suggested changes to the
author, and he could insert these into the manu¬
script, again via telephone.
Of course I am hoping that if any language
becomes standard it will be my TEX language.
Well. .. perhaps I am biased, and I know that
TEX provides only small refinements over what
is available in other systems. Yet several dozen
small refinements add up to something that is
important to me, and I think such refinement
might prove important to other people as well.
Therefore I’d like to spend the next few
minutes explaining more about TEX.
THE TEX INPUT LANGUAGE.
TEX must deal with “ordinary” text as well
as mathematics, and it is designed as a unified
system in which the mathematical features
blend in with the word-processing routines
instead of being “tacked on” to a conventional
typesetting language. The main idea of TEX is
to construct what I call boxes. A character of
type by itself is a box, as is a solid black rec¬
tangle, and we use such “atoms” to construct
more complex boxes analogous to “molecules,”
by forming horizontal or vertical lists of boxes.
The final pages of text are boxes made out of
lists of boxes made out of lists of boxes, and so
on down to the individual characters and black
rectangles which are not decomposed further;
for example, a typical page of a book is a box
formed from vertical lists of boxes representing
lines of type, and these lines of type are boxes
formed from a horizontal list of boxes repre¬
senting individual letters. A mathematical
formula breaks down into boxes in a natural
way; for example, the numerator and denomi¬
nator of a fraction are boxes, and so is the
bar line between them (since it is a thin but
solid black rectangle). The elements of a
rectangular matrix are boxes, and so on.
The individual boxes of a horizontal list
or a vertical list are separated by a special
kind of elastic mortar which I call “glue.” The
glue between two boxes has three component
parts (x, y, z) expressed in units of length:
the space component, x, is the ideal or
normal space desired between these
boxes;
the stretch component, y, is the amount of
extra space which is tolerable;
the shrink component, z, is the amount of
space which may be removed if
necessary.
Suppose the list contains n+1 boxes B 0 , Bj,
.... B n separated by n globs of glue having
specifications (xj, x lf z x ),... , (x n , y n , z n ).
When this list is made into a box, we set the
glue according to the desired final size of the
box. If the final size is to be larger than we
would obtain with the normal spacing Xj +
... + x n , we increase the space proportional
to the y’s so that the actual space between
boxes is
x t + ty!,..., x„+ ty n
for some appropriate t > 0. On the other hand
if the desired final size must be smaller, we
decrease the space to
Xl -tz 1 ,...,x n -tz n ,
in proportion to the individual shrinkages zj. In
the later case t is not allowed to become greater
than 1; the glue will never be smaller than
x - z, although it might occasionally become
greater than x + y. Once the glue has been set,
the box is rigid and never changes its size again.
Consider, for example, a normal line of text,
which is a list of individual character boxes.
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91
The glue between letters of a word will have
x = y = z = 0, say, meaning that this word
which is a list of individual character boxes.
The glue between letters of a word will have
x = y = z = 0, say, meaning that this word
always has the letters butting against each
other; but the glue between words might have
x equal to the width of the letter ‘e,’ and y = x,
and z = Vix, meaning that the space between
words might expand or shrink. The spaces after
punctuation marks like periods and commas
might be allowed to stretch at a faster rate but
to shrink more slowly.
An important special case of this glue
concept occurs when we have “infinite”
stretchability. Suppose the x and z components
are zero, but the y component is extremely
large, say y is one mile long. If such an element
of glue is placed at the left of a list of boxes,
the effect will be to put essentially all of the
expansion at the left, therefore the boxes will
be right-justified so that the right edge will be
flush with the margin. Similarly if we place
such infinitely stretchable glue at both ends of
the list, the effect will be to center the line.
These common typographic operations there¬
fore turn out to be simple special cases of the
general idea of variable glue, and the computer
can do its job more elegantly since it is dealing
with fewer primitives. Incidentally you will
notice from this example that glue is allowed
to appear at the ends of a list, not just between
boxes; actually it is also possible to have glue
next to glue, and boxes next to boxes, so that a
list of boxes really is a list of boxes and glue
mixed in any fashion whatever. I didn’t
mention this before, because for some reason it
seems easier to explain the idea first in the case
when boxes alternate with glue.
The same principles apply to vertical lists.
For example, the glue which appears above and
below a displayed equation will tend to be
stretchable and shrinkable, but the glue
between lines of text will be calculated so that
adjacent base lines will be uniformly spaced
when possible. You can imagine how the
concept of glue allows you to do special tricks
like backspacing (by letting x be negative), in a
natural manner.
LINE DIVISION.
One of the more interesting things a system
like TEX has to do is to divide up a paragraph
into individual lines so that each line is about
the right length. The traditional way to do this,
which is still used on today’s computer type¬
setting systems, is to make the best possible
line division you can whenever you come to the
right margin, but once this line has been output
you never reconsider it again-you start the
next line with no memory of what has come
before. Actually it often happens that one
could do better by moving a short word down
from one line to the next, but the problem is
that you don’t know what the rest of the para¬
graph will be like when you have only looked at
one line’s worth.
The TEX system will introduce a new
approach to the problem of line division, in
which the end of a paragraph does influence
the way the first lines are broken; this will
result in more even spacing and fewer hyphen¬
ated words. Here is how it works: First we
convert the line division problem to a precisely-
defined mathematical problem by using TEX’s
glue to introduce the concept of “badness.”
When a horizontal list of boxes has a certain
natural width w (based on the width of its
boxes and the space components of its glue),
a certain stretchability y (the sum of the stretch
components) and a certain shrinkability z (the
sum of the shrinkages), the badness of setting
the glue to make a box of width W is defir,ed
to be 1 + 100t 3 in our previous notation; more
precisely, it is
1
, ifW = w,
1 + ioo/ w_w Y
, if W> w ,
\ y /
1 + 10 o/ w-W Y
, ifw-z^W < w
V * t
infinite
, if W < w - z .
Thus if the desired width W is near the natural
width w, or if there is a lot of stretchability and
shrinkability, the badness rating is very small;
but if W is much greater than w and there isn’t
much ability to stretch, we have a lot of bad¬
ness. Furthermore we add penalty points to the
badness rating if the line ends at a compara¬
tively undesirable place; for example, when a
word needs to be hyphenated, the badness goes
up by 25, and an even worse penalty is paid if
we have to break up mathematical formulas.
The line division problem may now be
stated as follows. “Given the text of a para¬
graph and the set of all allowable places to
break it between lines, find breakpoints which
minimize the sum of the squares of the bad¬
nesses of the resulting lines.” This definition is
quite arbitrary, of course, but it seems to work.
Preliminary experiments show that the same
choice of breakpoints is almost always found
when simply minimizing the sum of the
individual badnesses rather than the sum of
their squares, but it seems wise to minimize the
sum of squares as a precautionary measure since
this will also tend to minimize the maximum
badness.
Just stating the line division problem in
mathematical terms doesn’t solve it, of course:;
we need to have a good way to find the desired
breakpoints. If there are n permissible places to
break (including all spaces between words and
all possible hyphenations), there are 2 n possible
ways to divide up the paragraph, and we would
never have time to look at them all. Fortu¬
nately there is a technique that can be used to
reduce the number of computational steps to
order n 2 instead of 2 n ; this is a special case of
what Richard Bellman calls “dynamic program¬
ming.” Let f(j) be the minimum sum of badness
squares for all ways to divide the initial text of
the paragraph up to breakpoint j, including a
break at j, and let b(i, j) be the badness of a
line which runs from breakpoint i to break¬
point j. Let breakpoint 0 denote the beginning
of the paragraph; and let breakpoint n + 1 be
the end of the paragraph, with infinitely
expandable glue inserted just before this final
breakpoint. Then
f(0) = 0 ;
f(j)= min (f(i) + b(i,j) 2 ),
0 < i < j
for 1 ^ j <Sn+l .
The computation of f(l).f(n+l) can be
done in order n 2 steps, and f(n+l) will be the
minimum possible sum of badnesses squared.
By remembering the values of i at which the
minima occurred for each j, we can find break¬
points which give the best line divisions, as
desired.
In practice we need not test extremely
unlikely breakpoints; for example, there is
rarely any reason to hyphenate the very first
word of a paragraph. Thus it turns out that this
dynamic programming method can be further
improved to an algorithm whose running rime
is almost always of order n instead of n , and
comparatively few hyphenations will need to
be tried. Incidentally, the problem of hyphen¬
ation itself leads to some interesting mathe¬
matical questions, but I don’t have time to
discuss them today. (Cf. [41] and the
references in that paper.)
The idea of badness ratings applies in the
vertical dimension as well as in the horizontal;
in this case we want to avoid breaking columns
or pages in a bad manner. For example, penalty
points are given for splitting a paragraph
between pages after a hyphenation, or for
dividing it in such a way that only one of its
lines-a so-called “widow” line—appears on a
page. The placement of illustrations, tables, and
footnotes is also facilitated by formularing
appropriate rules of placement in terms of bad¬
ness.
There is more to TEX, including for
example some facilities for handling the rather
intricate layouts often needed to typeset tables
without having to calculate column widths; but
I think I have described the most important
principles of its organization. During the next
few months 1 plan to write the computer pro¬
grams for TEX in such a way that each algo¬
rithm is clearly explained and so that the
system can be implemented on many different
computers without great difficulty; then I
intend to publish the programs in a book so
that everyone who wants to can use them.
ENTR’ACTE.
I said at the beginning that this talk would
be in two parts, discussing both the ways that
typography can help mathematics and that
mathematics can help typography. So far we
have seen a little of both, but the mathematics
has been comparatively trivial. In the remainder
of my lecture I would like to discuss what I
believe is a much more significant application
of mathematics to typography, namely to the
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Page 9
specification of the letter shapes themselves.
A more accurate way to describe the two parts
of my lecture would be to say that the first part
was about TEX, a system which takes manu¬
scripts and converts them into specifications
about where to put each character on each
page; and the second part will be about another
system I’m working on called METAFONT,
which generates the characters themselves,
for use in the inkier parts of the printing
business.
Before I get into the second part of my
lecture I need to discuss recent developments
in printing technology. The most reliable way
to print mathematics books of high quality
during the past several decades has been to use
the monotype process (actually the Monotype
Corporation now manufactures digital photo-
setting equipment as well as the traditional
‘monotype’ machines) which casts characters
in hot lead, together with hand operations for
complex built-up formulas. When I watched
this process being applied to my own books
several years ago, I was surprised to learn that
the lead type was used to print only one copy;
this master copy was then photographed, and
the real printing took place from the photo¬
graphic plates. This somewhat awkward
sequence of steps was justified because it was
the best way known to give good results.
During the 1960’s, however, hot lead type was
replaced for many purposes by devices like the
Photon machine used to prepare the printed
programs for this lecture; in this case the
proi:ess is entirely photographical, since the
letter shapes are stored as small negatives on
a rotating disk, and the plates needed for
printing are obtained by exposing the film
after transforming the characters into the
proper size and position with mirrors and
lenses (cf. [10]). Such machines are limited
by slow speed and the difficulties of adding
new characters.
‘THIRD-GENERATION”
TYPESETTING EQUIPMENT
More recent machines, such as the one used
to prepare the current volumes of the Trans¬
actions, have replaced these “analog” processes
by a “digital” one. The new idea is to divide the
page or the photographic negative into millions
of liny rectangles, like a piece of graph paper or
like a television screen but with a much higher
resolution of about 1000 lines per inch. For
each of the tiny “pixels” in such a raster
pattern-there are about a million square pixels
in every square inch-the typesetting machine
decides whether it is to be black or white, and
the black ones are exposed on the photographic
plate by using a very precisely controlled
electron beam or laser beam. Since these
machines have few moving parts and require
little or no mechanical motion, they can
operate at very high speeds even though they
are exposing only a tiny bit of the film at any
time.
Stating this another way, the new printing
equipment essentially treats each page of a
book as a huge matrix of 0’s and l’s, with ink
to be placed in the positions that are 1 while
the 0 positions are to be left blank. It’s like the
flashcards at a football stadium, although on a
much grander scale. The total job of a system
like TEX now becomes one of converting an
author’s manuscript into a gigantic bit matrix.
The first question we must ask of course is,
“What happens to the quality?” Clearly a
television picture is no match for a photograph,
arid the digital typesetting machines would be
quite unsatisfactory if their output looked
inferior to the results obtained with metal
type. In matters like this, I have to confess
being somewhat of a stickler and a perfec¬
tionist; for example, I refuse to eat margarine
instead of butter, and I have never heard an
electronic organ that sounds even remotely as
beautiful as a pipe organ. Therefore I was quite
skeptical about digital typography, until I saw
an actual sample of what was done on a high
quality machine and held it under a magnifying
glass: It was impossible to tell that the letters
were generated with a discrete raster! The
reason for this is not that our eyes can’t distin¬
guish more than 1000 points per inch; in
appropriate circumstances they can. The
reason is that particles of ink can’t distinguish
such fine details-you can’t print the edge of
an ink line that zigzags 1000 times on the
diagonal of a square inch, the ink will round
off the edges. In fact the critical number
seems to be more like 500 than 1000. Thus
the physical properties of ink cause it to appear
as if there were no raster at all.
It now seems clear that discrete raster-based
printing devices will soon make the other
machines obsolete for nearly all publishing
activity. Thus in future days the fact that
Gutenberg and others invented movable type
will not be especially relevant, it will merely
be a curious historical fact which influenced
history for only about 500 years. The ulti¬
mately relevant thing will be mathematics: the
mathematics of matrices of 0’s and l’s!
SEMI-PHILOSOPHICAL REMARKS.
I have to tell the next part of the story from
my personal point of view. As a combinatorial
mathematician, I really identify with matrices
of 0’s and l’s, so when I learned last spring
about such printing machines it was impossible
for me to continue what I was doing; I just had
to take time off to explore the possibilities of
the new equipment. My motivation was also
increased by the degradation of quality I had
been observing in technical journals; and
furthermore the publishers of my books on
computer programming had tried valiantly but
unsuccessfully to produce the second edition
of volume 2 in the style of the first edition
without using the rapidly-disappearing hot lead
process. It appeared that my books would soon
have to look as bad as the journals! When 1 saw
that these problems could all be solved by
appropriate computer programming, I couldn’t
resist trying to find a solution by myself.
One of the most important factors in my
motivation was the knowledge that the problem
would be solved once and for all, if I could find
a purely mathematical way to define the letter
shapes and convert them to discrete raster
patterns. Even though new printing methods
are bound to be devised in the future, possibly
even before I finish volume seven of the books
I’m writing, any new machines axe almost
certain to be based on a high precision raster;
and although the precision of the raster may
change, the letter shapes can stay the same
forever, once they are defined in a machine-
independent form. My goal was therefore to
give a precise description of the shapes of all
the symbols I would need.
I looked at the way fonts of the type are
being digitized at several places in different
parts of the world; it is basically done by
taking existing fonts and copying them using
sophisticated camera equipment and computer
programs, together with manual editing. But
this seemed instinctively wrong to me, partly
because the sophisticated equipment wasn’t
readily available in our laboratory at Stanford,
and partly because the copying of copyrighted
fonts is of questionable legality, but mostly
because I felt that the whole idea of making a
copy was not penetrating to the heart of the
problem. It reminded me of the anecdote I had
once heard about slide rules in Japan.
According to this story, the first slide rule ever
brought to the Orient had a black speck of dirt
on it; so for many years all Japanese slide rules
had a useless black spot in this same position!
The story is probably apocryphal, but the
point is that we should copy the substance
rather than the form. I felt that the right
question to ask would not be “How should
this font of type be copied?” but rather:
“If the great type designers of the past were
alive today, how would they design fonts for
the new equipment?”- I didn’t expect to be
capable of finding the exact answer to this
question, of course, but I did feel that it would
lead me in the right direction, so I began to
read about the history of type design.
Well, this is a most fascinating subject, but
I can’t talk much about it in a limited time.
Two of the first things I read were autobio¬
graphical notes by two well-known 20th
century type designers, Hermann Zapf [51]
and Frederic W. Goudy [20], and I was espe¬
cially interested by some of Zapfs remarks:
With the beginning of the ’sixties ... I
was stimulated by this new field [photo-
composing] ... The type-designer — or
better, let us start calling him the alpha¬
bet designer-will have to see his task
and his responsibility more than before
in the coordination of the tradition in
the development of letterforms with the
practical purpose and the needs of the
advanced equipment of today ... The
new photocomposing systems using
cathode-ray tubes (CRT) or digital
storage for the alphabet bring with them
some absolutely new technical problems,
many more than did the past ... [51,
P-71].
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 10
Number 43
93
I have the impression that Goudy would not
have been so sympathetic to the new-fangled
equipment, yet his book also gave helpful ideas.
MATHEMATICAL TYPE DESIGN.
Fortunately the Stanford Library has a
wonderful collection of books about printing,
and I had the chance to read many rather rare
source materials. I learned to my surprise that
the idea of defining letters mathematically is
by no means new, it goes back to the fifteenth
century and it became rather highly developed
in the early part of the sixteenth. This was the
time when there were Renaissance men who
combined mathematics with the real world, and
in particular there was an interest in con¬
structing capital letters with ruler and compass.
The first person to do this was apparently
Felice Feliciano, about 1460, whose hand¬
written manuscript in the Vatican Library was
published 500 years later [19]. Feliciano was
an excellent calligrapher who wanted to put the
principles of calligraphy on a sound mathemat¬
ical foundation. Several other fifteenth-century
authors made similar experiments ([8] gives a
critical summary of these early developments),
but the most notable work of this kind
appeared in the early sixteenth century.
The Italian mathematician Luca Pacioli,
who had previously written the most influential
book on algebra at the time (one of the first
algebra books ever published), included an
appendix on alphabets in his De Devina Pro-
portione, a book about geometry and the
“golden section” which appeared in 1509.
Another notable Italian work on the subject
was published by Francesco Tomiello in 1517
[48], [33]; Fig. 4 illustrates the letter B as con¬
structed by Pacioli, Tomiello, and by Giovan-
battista Palatino [43]. Palatino was one of the
best calligraphers of the century, and he did
this work about 1550. Similar work appeared in
Germany and France; the German book was
probably the most famous and influential, it
was Albrecht Durer’s Underweysung der
Messung [18], a manual of instruction in
geometry for Renaissance painters. The French
book was also rather popular, it was Champ
Fleury by Geofroy Tory [49], the first royal
printer of France and the man who introduced
accented letters into French typography. Fig. 5
shows Tory’s two suggestions for the letter B.
Of all these books I much prefer Torniello’s,
since he was the only one who stated the con¬
structions clearly and unambiguously.
Apparently nobody carried this work
further to lower case letters, numerals, or italic
letters and other symbols, until more than 100
years later when Joseph Moxon made a detailed
study of some beautiful letters designed in
Holland [38]. The ultimate in refinement of
this mathematical approach took place shortly
afterwards when Louis XIV of France commis¬
sioned the creation of a Royal Alphabet. A
commission of artists and typographers worked
on Louis’ project for more than ten years
beginning about 1690, and they made elaborate
constructions such as those shown in Fig. 6
[24],
4-
(c)
Figure 4. Sixteenth century ruler-and-compass constructions for the letter B by (a) Pacioli
[42], (b) Tomiello [48] , and (c) Palatino [43] .
Figure 5. Two more B's, by Tory [49].
Number 43
94
Dr. Dobb's Journal of Computer Calisthenics 8i Orthodontia, Box E, Menlo Park, CA 94025
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T’hus it is clear that the mathematical
definition of letter forms has a long history.
However, I must also report near-universal
agreement among today’s scholars of typog¬
raphy that those efforts were a failure. At
worst, the ruler-and-compass letters have been
called “ugly” and at best they are said to be
“deprived of calligraphic grace” [8], The
French designs were not really followed faith¬
fully by Phillipe Grandjean who actually cut
Louis XIV’s type, nor by anybody else to date,
and F. W. Goudy’s reaction to this was: “God
be praised!” [20, p. 139]. Such strictly geo¬
metric letter forms were in fact criticized
already in the sixteenth century by Giovan
Cresci, a noted scribe at the Vatican Library
and the Sistine Chapel. Here is what Cresci
wrote in 1560:
Well, Cresci was right. But fortunately there
have been a few advances in mathematics
during the last 400 years, and we now have
some other tricks up our sleeves besides straight
lines and circles. In fact, it is now possible to
prescribe formulas that match the nuances of
the best type designers; and perhaps a talented
designer working with appropriate mathemat¬
ical tools will be able to produce something
even better than we now have.
DEFINING GOOD CURVES.
I have come to the conclusion that if Euclid,
tihe prince of geometry, returned to this
world of ours, he would never find that the
curves of the letters could be constructed by
means of circles made with compasses. [16]
Let’s consider the following mathematical
problem: Given n points Zj, z 2 .z n in the
plane, what is the most pleasing closed curve
that goes through them in the specified order
Z], Z 2 ,..., z n and then returns to zi? To
avoid degenerate situations we may assume that
n is at least 4. This problem is essentially like
the dot-to-dot puzzles that we give to young
children.
Of course it is not a well-posed mathemat¬
ical problem, since I didn’t say what it means
for a curve to be “most pleasing”. Let’s first
postulate some axioms that the most pleasing
curve should satisfy.
Property 1 (Invariance). If the given points
are rotated, translated, or expanded, the most
pleasing curve will be rotated, translated, or
expanded in the same way. [In symbols:
MPC(azi +b,..., az n + b) = aMPC(Zi,.. ,z n )
+ b.]
Property 2 (Symmetry). Cyclic permutation
of the given points does not change the solu¬
tion, [MPC(z!,z 2 .z n ) = MPC(z 2 ,...,
z n> 2 i )•]
Property 3 (Extensionality). Adding a new
point that is already on the most pleasing curve
does not change the solution. [If z is between
zfc and z^+ 1 on MPC(zi,. .. ,z n ), then
MPC(zi.... .Zk.z.zk+j,... ,z n ) = MPC
(Zj,... .zjc.zjj+j,... ,Zn).]
(to)
Figure 6. Roman and italic letters designed for Louis XIV of France [24].
These properties are rather easy to justify on
intuitive grounds. For example, the exten-
sionality property says that additional infor¬
mation won’t lead to a poorer solution.
The next property is not so immediately
apparent, but I believe it is important for the
application I have in mind.
Property 4 (Locality). Each segment of the
most pleasing curve between two of the given
points depends only on those points and the
ones immediately preceding and following.
[MPC(Zi ,z 2 .Zj,) is composed of
MPC(z n ,zi,z 2 ,z 3 ) from zj to z 2 , then
MPC(zj ,z 2 ,z 3 ,Z 4 ) from z 2 to z 3 ,..., then
MPC(z n _ 1 ,z n ,z 1 ,z 2 ) from zn to Zj.]
According to the locality property, changes to
one part of a pattern won’t affect the other
parts. This simplifies our search for the most
pleasing curve, because we need only solve the
problem in the case of four given points; and
experience shows that it is also a great simpli¬
fication when letters are being designed, since
individual portions of strokes can be dealt with
separately. Incidentally, property 4 implies
property 2 (cyclic symmetry).
One way to satisfy all four of these prop¬
erties is simply to let the most pleasing curve
consist of straight line segments. But this
doesn’t seem adequately pleasing, so we
postulate:
Property 5 (Smoothness). There are no
sharp comers in the most pleasing curve.
[MPC (Zj ,..., z n ) is differentiable, under some
parameterization.] In other words, there is a
unique tangent at every point of the curve.
The extensionality, locality, and smoothness
properties taken together imply, in fact, that
the direction of the tangent at z 2 depends only
on z 1 , z 2 , and z 3 . For this tangent appears in
two curves, the one from zi-_ 2 to z^ and the
one from zfc to z^+j, hence we know that it
depends only on (zk- 2 ,zi c _ 1 ,zi c ,z) c +i) and
C jiutnu turn d< la Iftnx A —
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Page 12
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
95
and that it depends only on (%-1 .z^.z^+i,
zk+ 2 ). By the extensionality property, we can
assume that n is at least 5, so Zk _ 2 is different
from zjc +2 and the tangent must be independ¬
ent of them both. We have actually used only a
very weak form of extensionality in this
argument.
If we apply the full strength of the ex¬
tensionality postulate, we obtain a much
stronger consequence, which is quite un¬
fortunate: There is no good way to satis¬
fy Properties 1-5! For example, suppose we
add one more axiom, which is almost necessary
in any reasonable definition of pleasing curves:
Property 6 (Roundness). If Zj, z 2 , z 3 , Z 4 are
consecutive points of a circle, the most pleasing
curve through them is that circle. This property
together with our previous observation about
the tangent depending only on three points
completely determines the tangent at each of
our given points; namely, the tangent at Zfc is
the tangent to the circle which passes through
Zfc_!, zk, and z^+i. (Let’s ignore for the
moment the possibility that these three points
lie on a straight line.) Now the extensionality
property says that if z is any point between Z\
and z 2 on the most pleasing curve for
Zj,... ,z n , we know the tangent direction at
z, as long as z is not the line from z\ to z 2 . But
there is a unique curve starting at any z off this
line and having the specified tangents at each of
its points, namely the arc of the circle from z to
z 2 passing through Z \: No matter where you
start, off the straight line, there is only one
curve having the correct tangents. It follows
that the tangent at z 2 depends only on z\, z 2
and the tangent at Zj, and this is impossible.
The above argument proves that there is no
way to satisfy properties 3, 4, 5, and 6 . A sim¬
ilar argument would show the impossibility for
any reasonable replacement for property 6 ,
since the tangents determined for all z between
Zi and z 2 will define a vector field in which
there are unique curves through essentially all
of the points z, yet a two-parameter family of
curves is required between Z\ and z 2 in order
to allow suficient flexibility in the derivatives
there.
So we have to give up one of these proper¬
ties. The locality property is the most
suspicious one, but I mentioned before that I
didn’t want to give it up; therefore the ex¬
tensionality property has to go. This means that
if we take the most pleasing curve through
Zi.z n and if we specify a further point
z actually on this curve between z^_ l and zfc,
where the tangent at z is not the same as the
tangent to the circle from zj[_ j to z to z^,
then the “most pleasing” curve through these
n+1 points will be different. A possible virtue is
that we are encouraged not to specify too many
points; a possible drawback is that we may not
be able to get the curves we want.
A PRACTICAL APPROXIMATION.
Returning to the question of type design,
our goal is to specify a few points and to
have a mathematical formula that defines a
pleasant curve through these points; such curves
will be used to define the shape of the character
we are designing. Ideally it should also be easy
to compute the curves. I decided to use cubic
equations
z(t) = a 0 + <* 11 + a 2 t 2 + a 3 t 3
where a 0 , a lt a 2 , a 3 are complex numbers
and t is a real parameter. The curves I am
dealing with are cubic spines, namely piece-
wise cubic equations, since a different cubic
will be used in each interval between two of the
given points; however, the way I am deter¬
mining the coefficients of these two cubics is
different from any of the methods known to
me, in my limited experience with the vast
literature about spines. Perhaps my way to
choose the coefficients is more awkward than
the usual ones; but I have obtained good results
with it, so I’m not ashamed to reveal the
curious way I proceeded.
In the first place, I decided that the cubic
equation between Z\ and z 2 should be deter¬
mined completely by Zj and z 2 and the direc¬
tions of the tangents at Zj and z 2 . We have
already seen that these tangents are essentially
predetermined if properties 4, 5, and 6 are to
be valid, and I have also found frequent occa¬
sion in type design when it was desirable to
specify that a certain tangent was to be made
horizontal or vertical. Thus, my method of
computing a nice curve through a given se¬
quence of points is first to compute the tangent
directions at each point, then to compute the
cubics in each interval based solely on the end¬
points of that interval and on the desired
tangents there. By rotation and translation and
scaling, according to property 1 , we can assume
that the problem is to go in the complex pliine
from 0 to 1 , with given directions at the end¬
points. The most general cubic equation which
does this is
z(t)= 3t 2 -2t 3 +re i 6 t(l-t ) 2
+ se ~ * 0 t 2 (1 — t) ,
and it remains to determine positive numbers
r and s as appropriate functions of 9 and 0.
In the second place, I realized that it was
impossible to satisfy property 6 with cubic
splines, because you can’t draw a circle as a
cubic function of t. But I wanted to be able to
get curves that were as near to being circles
as possible, whenever four consecutive data
points lay on a circle; the curves should prefer¬
ably be indistinguishable from circles as far
as the human eye is concerned. Therefore when
9 = 0 I decided to choose r = s in such a way
that z( 1 / 2 ) was precisely on the relevant circle,
hoping that the curve between 0 and 1/2
and between 1/2 and 1 wouldn’t veer too
far away. Well, this turned out to work ex¬
tremely well: A little calculation, done with the
help of a computer, (thanks are due to the
developers of the computer algebra system
called MACSYMA at MIT, and to the ARPA
network which makes this system available
for research work) showed that the maximum
deviation from a true circle occurs at the points
t = (3 and the relative error is negli¬
gibly small. For example, if we take four points
equally spaced at distance 1 from some center,
the spline curve defined by these points in the
above manner stays between distance 1 and
distance 71/54 - 2v^/9 <1.00055 from the
center, an error of less than one part in a thou¬
sand: if there are 8 points, the maximum error
is less than four parts per million; and if there
are n points, the maximum error goes to zero
as 1 /n .
(Changing the notation slightly, let
2 ( 1 ) « I + (t le - l)(3t ! -2t’) + 411(1-0(1 -1-c iB t) (sin|^/|'l + “ s |)
and f(t) * |z(l)| a . Then
/cos0-l\ 1
f’(l) - 8sin’2 I _ ! _I <t-l)t( 2 t-l)( 6 l ’-61 + 1)
H-/
and
"»« U(l)l •
0<t<l
,/wn . 1 +
\ 6 / 55296
while minQ <t < 1 |z(t)| = z ( 0 ) = z(l/ 2 ) =
z(l)=l. The “ two-point circle” has max
|z(t) |= \/28/27 = 1.01835, the three-point
circle has max | z(t) | = \/325/324 = 1.001542,
and the eight-point circle has max |z(t) | =
1.0000042455 .)
Another case when a natural way to choose
r and s suggests itself is when 0 + 0=90 ;
then the curve z(t) should be nearly the same as
an ellipse having the endpoints on its axes.
So far therefore I knew that I wanted
_4 _
I + COS 0
when 0 =
0 ;
. 4 cos 9
(I + cos 45 ® )(cos 45 °)
So I tried the formulas
4 cos 0
(I + cos 45 °)(cos 45 °)
when 0 -I- 0 ■ 90 °
So I tried the formulas
which fit both cases. However, this didn’t give
satisfactory results, especially when 0 + 0
approached 180 . My second attempt was
4 sin 0
and this has worked very well. Fig. 7 shows
the spline curves that result from the above
approach when 0 = 60 and when 9 varies from
0° to 120° in 5° steps.
It can be proved that if 9 and 0 are non-
negative and less than 180 , the cubic curve
z(t) I have defined will never cross the striaght
lines at angles 9 and 0 that meet the endpoints
0 and 1 respectively. This is a valuable pro¬
perty in type design, since it can be used to
guarantee that the curve won’t get out of
bounds. However, I found that it also led to
unsatisfactory curves when one of 0 or 0 was
very small and the other was not, since this
meant that the curve z(t) would be very
close to a straight line yet it would enter that
line from outside at a rather sharp angle In
fact, the angle 9 is not infrequently zero,
and this forces a straight line and a sharp
comer at the right endpoint. Therefore I
Number 43
96
Or. Dobb's Journal of Computer Calisthenics 8t Orthodontia, Box E, Menlo Park, CA 94025
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Figure 13. Different styles of type: (a) conventional "modern" font; (b) corresponding boldface; (c) sans serif font; (d) boldface
sans serif; (e) typewriter imitation with fixed width letters; (f) slanted letters; (g) caps and small caps; (h) "small lower
case"; (i) variations.
design each size of type individually. I’m not
claiming that Fig. 14 shows the best way for
the proportions to vary, it will take further
experimentation before I have a good idea of
what is desirable. The point I wish to make is
that the alteration of type sizes for subscripts
and so on is not as simple as it might seem at
first, but a system like METAFONT will be
able to vary the parameters quite readily, and
visual experiments on different parameter
settings can be carried out quickly. It used to
tale months for a type designer to make his
drawings and have them converted to metal
molds before he could see any proofs. One of
the results was that there simply wasn’t time
to give proper attention to all the mathemat¬
ical symbols and Greek letters, etc., as well
as to the more common symbols, so a printer
of mathematics had to make to with a hodge¬
podge of available characters in different sizes.
(For example, he was often obliged to use dif¬
ferent styles of letters in subscript positions, as
we have seen.) Under the approach I am rec¬
omending, we automatically get consistency of
all the symbols whenever the parameters
change.
FROM CONTINUOUS TO DISCRETE.
The METAFONT system must not only
define the characters in the continuum on the
plane, it must also express them in terms of a
discrete raster. Such squaring off of letters on
graph paper has a long history, going back far
before the invention of computers or television;
for example, we all can remember seeing cross-
stitch embroidery samplers from the nineteenth
century. The same idea on a finer scale has been
used in tapestries for many centuries: In our
home library, my wife found the example of
Fig. 15 which was woven in the northern part
of Norway about 1500; this shows the name of
St. Thomas in a style imitating contemporary
Figure 14. Adjusting the letters to coarser rasters.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
97
changed the formulas by making sure that both
r and s are always 1/2 or greater unless spe¬
cial exceptions are made; furthermore I never
let r or s exceed 4. Fig. 8 shows the spline
curves obtained under the same conditions as
Fig. 7, but with s set to 1/2 if the above
formula calls for any smaller value.
Using these techniques we obtain a system
for drawing reasonably nice curves, if not the
most pleasing ones, and it is especially good at
circles. If the method gives the wrong tangent
direction at some point, you can control this
by specifying two points very close together
having the desired slope. I have also included
another way to modify the standard tangent
directions, intended to make the system as
good at drawing ellipses as it is at drawing
circles: Before computing the splines I first
shrink the entire figure in the vertical direc¬
tion by muliplying all the y coordinates by a
given aspect ratio (normally 1); then the splines
are calculated, and the resulting shrunken
curves are stretched out again by dividing the
y coordinates by the aspect ratio.
Figure 7. Spline curves with 0 = 0° (5 ) 120°
and </> = 60 f
Figure 8. Same as Figure 7 but adjusted so
that r' = min04,r), s'= min (’/4,s).
APPLICATION TO TYPE DESIGN.
Now let’s take a closer look at what can be
drawn with a mathematical system like this. I
suppose the natural thing to show you would
be the letters A to Z; but since this is a math¬
ematical talk, let’s consider the digits 0 to 9
instead. (See Fig. 9.) Incidentally, the way I
have arranged these numerals illustrates a
fundamental distinction between a mathema¬
tician and a printer: the mathematician puts 0
next to the 1, but the printer always puts it
next to the 9.
Most of these digits are drawn by using
another idea taken from the history of typo¬
graphy, namely to imitate the calligrapher who
uses pen and ink. Consider first the numeral ‘3’,
for example: The computer program which
drew this symbol in Fig. 9 can be paraphrased
Figure 9. Digits 0 to 9 drawn by the META
FONT programs. (Further refine¬
ments to these characters will be
made before the font has its final
form.)
as follows. “First draw a dot whose left bound¬
ary is 1/6 of the way from the left edge to the
right edge of the type and whose bottom
boundary is 3/4 of the way from the top to the
bottom of the desired final shape. Then take a
hairline pen and, starting at the left of the dot,
draw the upward arc of an ellipse; after
reaching the top, the pen begins to grow in
width, and it proceeds downward in another
ellipse in such a way that the maximum width
occurs on the axis of the ellipse, with the right
edge of the pen 8/9 of the way from the left
edge to the right edge of the type. Then the pen
width begins to decrease to its original size
again as the pen traverses another ellipse taking
it down to a position 48% of the way from
the top to the bottom of the desired final
shape. ...”
Notice that instead of describing the bound¬
ary of the character, as the renaissance geo¬
meters did, my METAFONT system describes
the curve traveled by the center of the pen, and
the shape of this pen is allowed to vary as the
pen moves. The main advantage of this ap¬
proach is that the same definition readily yields
a family of infinitely many related fonts of
type, each font being internally consistent. The
change in pen size is governed by cubic splines
in a manner analogous to the motion of the
pen’s center. In order to define the 20 or so dif ¬
ferent type fonts used in various places in my
books, I need for the most part to use only
three kinds of pens, namely (i) a circular pen,
used for example to draw dots and at the base
of the numeral ‘7’; (ii) a horizontal pen, whose
shape is an ellipse, the width being variable but
the height being constantly equal to the height
of a hairline pen - such a pen is used most of
the time, and in particular to draw all of the
numeral ‘3’ except for the dots; (iii) a vertical
pen, analogous to the horizontal one, used for
example to draw the strokes at the bottom of
the ‘2’ and at the top of the ‘5’ and the ‘7’.
For the fonts I am using, it was not necessary
to use an oblique pen (i.e., an ellipse that is
tilted on its side) except to make the tilde
accent for Spanish n’s; but to produce fonts of
type analogous to Times Roman, an oblique
pen would of course be used. If this system
were to be extended to Chinese and Japanese
characters, I believe it would be best to add
another degree of freedom to the pen’s motion,
allowing an elliptical pen shape to rotate as well
as to change its width.
The digit ‘4’ shows another aspect of the
METAFONT system. Although this character
is fairly simple, consisting entirely of straight
lines, notice that the thick line has to be cut
off at an angle at the top. In order to do this,
there are erasers as well as pens. First the
computer draws a thick line all the way from
top to bottom, like the upper case letter ‘I’,
then it takes an eraser which erases everything
to its left and comes down the diagonal stroke,
then it takes a hairline pen and finishes the
diagonal stroke. Such an eraser is used also at
the top of the ‘1’ and the bottom of the V,
etc.
Sometimes a simple spline seems to be in¬
adequate to describe the proper growth of pen
width, so in a few cases I had to resort to de¬
scribing the left and right edges of the pen as
separate curves, to be filled in afterwards. This
occurs for example in the main stroke of the
numeral ‘2’, whose edges are defined by two
splines having a specified tangent at the bottom
and having vertical slope at the right of the
curve.
With these techniques I found that it was
possible to define a decent-looking complete
font, containing a total of 128 characters, in
about two months, although it will still be
necessary of course to do fine tuning when
more trail pages are typeset. (See Fig. 10.) The
most difficult symbol by far, at least for me,
was the letter S ( and the numeral 8, which uses
the same procedure); in fact I spent three days
and nights without sleep, trying to make the S
look right, before I got it. At one point I even
felt it would be easier to rewrite all my books
without using any S’s! After the first day of
discouraging trials, I showed what I had to my
wife, and she said, “Why don’t you make it S-
shaped?”
0ABCDEFGHIJKLMN
OPQRSTUVWXYZ[“]-
‘abcdefghijklmno
pqrstuvwxyzfffiflffiffl aelihoe/ELfXCE
0123456789:;<=>? *
r<;G%ic'()*+,-./ rA©Asnr:r<t>nij
Figure 10. A font of 128 characters defined
by METAFONT with standard
pen settings. (The accent charac¬
ters will be appropriately raised
and centered over other letters
when used by TEX.)
Fig. 11 shows how this problem was solved
by Pacioli, Torniello, Palatino, and the French
academicians; but the letter doesn’t look like a
modern S. Furthermore I think the engraver of
the French S cheated a little in rounding off
some lines near the middle — perhaps he used a
French curve. With my wife’s assistance, I
finally came up with a satisfactory solution,
somewhat like those used in the sixteenth
century but generalized to ellipses. Each
boundary of each arc of my S curve is com¬
posed of an ellipse and a straight line, deter¬
mined by (i) the locations of the beginning and
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Dr. Dobb's Journal of Computer Calisthenics 8t Orthodontia, Box E, Menlo Park, CA 94025
Number 43
ending points, (ii) the slope of the straight line,
and (iii) the desired left extremity of the
curve. It took me three hours to derive the
necessary formulas, and I think Newton and
Leibnitz would have enjoyed working on this
problem. Fig. 12 shows various trial S’s drawn
by this scheme with different slopes; I hope
you prefer the middle one, since it is the one
I am actually using.
Figure 12 Different S's obtained by varying
the slope in the middle. (This
shows 1/2, 2/3, 3/4, 1, 4/3, 3/2,
and 2 times the "correct" slope.)
FAMILIES OF FONTS.
To extend the METAFONT system, one
essentially writes a computer program for the
description of each character, in a special lan¬
guage intended for describing pen and eraser
strokes. My colleage R. W. Gosper has observed
that this is the opposite of Sesame Street:
Instead of ‘This program was brought to you
by the letter S” we have ‘This letter S was
brought to you by a program.” There are about
20 parameters to the program, telling how big a
hairline pen is, how wide it whould be when
drawing straight or curved stem lines, and
specifying the sizes and proportions of various
parts of the letters (the x-height, the heights of
ascenders and descenders, the set width, the
length of serifs, and so forth). By changing
these parameters, we obtain infinitely many
different styles of type, yet all of them are
related and they seem to blend harmoniously,
with each other.
For example, Fig. 13 shows some of the
possibilities. In Fig. 13a we have a conventional
“modem” font in the tradition of Bodoni and
Bell and “Scotch Roman”. Then Fig. 13b
shows a corresponding boldface, in which the
hairlines are slightly larger and the stem lines
are substantially wider. By making the hairlines
and stem lines both the same size, and setting
the serif length to zero, we obtain a sans serif
font as shown in Fig. 13c. All of these examples
are produced with the same programs defining
the letter shapes; only the parameters are being
varied. Actually the particular font shown in
Fig. 13c will have a different style of g, because
the descenders are especially short in this font,
but I have shown this “g” in order to illustrate
the parametric variations. Fig. 13d shows a
boldface sans-serif style in which the pen has
an oval shape wider than it is tall; I find this
style especially pleasing, particularly because it
came out by accident — I designed the
programs only so that two or three different
fonts would look right, all the others are free
bonuses, and I had no idea that this one would
be so nice.
With a suitable setting of the parameters,
we can even imitate a typewriter with its
fixed width letters, as shown in Fig. 13e. There
is also a provision to slant the letters as in Fig.
13f; here the pen position is varied, but the
actual shape of the pen is not being slanted,
so circles remain circles.
Another setting of the parameters leads to
caps and small caps as shown in Fig. 13g; small
caps are drawn with the pens and heights or¬
dinarily used for lower case letters, but con¬
trolled by the programs for upper case letters.
Fig. 13h shows something printers have never
seen before: this is what happens when you
draw lower case letters in the small caps style,
and we might call it “small lower case”. It
actually turns out to be one of the most
pleasing fonts of all, except that the dots are
too large.
Finally, Fig. 13i illustrates the variations
you can get by giving weirder settings to the
parameters.
When I was an assistant professor at Caltech,
the math department secretaries used to send
occasional “crank” visitors to my office, and
I recall one time when a man came to ask if
anybody had calculated the value of 7 T “out to
the end” yet. I tried to explain to him that 7T
had been proved irrational, but this didn’t seem
to sink in, so finally I showed him a table of 7T
to 100,000 decimals and told him that the
expansion hadn’t ended yet. I wish I could have
had my typographical system ready at that
time, so that I could have shown him Fig. 14!
Fig. 14 illustrates another principle of type
design, namely that different sizes of type in
the same style are not simply obtained from
each other by optical transformations. The
heights and widths and pen stroke sizes change
at different rates, and a good typographer will
Number 43
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 15
99
Figure 15. Lettering equivalent to this raster pattern appears in a Norwegian tapestry from
Gildeskaal old church, woven about 1500 [22, p. 116].
calligraphy, and I’m sure that examples which
antedate the printing press can be found
elsewhere.
Fig. 16 shows how METAFONT produces
the same letters from the same parameters but
with different degrees of resolution in the
raster. This digitalization process itself is
considerably more difficult than it may seem at
first, and some nontrivial mathematical
concepts were needed before I could produce
satisfactory results. In the first place, it is not
sufficient merely to draw or to imagine drawing
the character with infinite precision and then to
“round” it by blacking in all the squares on
graph paper that are sufficiently dark in the
true image. One of the reasons this fails is that
the three stem lines of the m, for instance,
might be located in different relative positions
with respect to the grid, so that the first stroke
might round to three units wide (say) and the
second might round to four. This would be
quite unsatisfactory, as the eye quickly picks
up such a variation in thickness, but it is
avoided by METAFONT since the pen itself is
first digitized and then the same digitized pen is
used for all three strokes. Another problem is
that those three strokes should be equally
spaced; it would look bad if there were seven
units between the first two and eight units
between the last two, so the program for ‘m’
needs to round its points in such a way that
this doesn’t happen.
The process of digitizing the pen is not
trivial either. Suppose, for example, we want a
circular pen that is 2 raster units wide; the
appropriate pen is clearly 2X2 square, which
is the closest to a circle that we can come at
this low degree of resolution. Now notice that
we can’t center a 2 X 2 square on any particular
square, since none of the four squares is at its
center; the same problem arises whenever we
have to deal with a pen having even dimensions.
One way to resolve this would be to insist on
working only with odd numbers, but this would
be far too limiting; so METAFONT uses a
special rounding rule for the position of the
pen’s center. In general, suppose the pen is an
ellipse of integer width w and integer height h;
then if the pen is to be positioned at the real
coordinates (x, y), its actual position on the
discrete grid is taken to be
(Lx -6 (w) J,|_y-5 (h) J)
where L x J denotes the greatest integer less
than or equal to x, and 6 (even) = %, 6 (odd) =
0. The pen itself, if positioned at the origin,
would consist of all integers (x, y) which
satisfy
^ 2(x-8(»)) j ’ + ^ 2(y-6Ql)) ^ ’<!+„„ ^ 28 (w) 2*(h)^ 1
This formula-which incidentally is not the
first one I tried-ensures that the discrete pen
will indeed be w units wide and h units high.
when w and h are positive integers. Fig. 17
shows the pens obtained for small w and h.
Still another problem appears when we want
curved lines to look right. Fig. 18(a) shows a
semicircle of radius 10 units, drawn with a pen
of height 1 and width 3, when the right
boundary of the pen falls exactly at an integer
point; the pen sticks out terribly in one place.
On the other hand if this right boundary falls
just shy of an integer point, we get the curve in
Fig. 18(b) which looks too flat. The ideal
occurs in Fig. 18(c), when the right boundary
occurs exactly midway between integers. There¬
fore the METAFONT programs adjust the
location of curves to the raster before actually
drawing the curves, forcing the favorable
situation of Fig. 18(c); the actual shape of each
letter changes slightly in order to adapt that
letter to the desired raster size in a pleasant
way.
There is yet another problem, which arises
when the pen is growing in such a way that the
edges of the curve it traces would be mono¬
tonic if the pen were drawn to infinite preci¬
sion, yet the independent rounding of pen
location and pen width causes this mono ton¬
icity to disappear. The problem arises only
rarely, but when it does happen the eye
immediately notices it. Consider, for example,
the completely linear situation in Fig. 19,
where each decrease by one unit in y is
accompanied by an increase of .3 units in x and
an increase of .2 units in the pen width w; the
intended pen height is constant and very small,
but in the discrete case the pen height is taken
to be 1. The lightly shaded portion of Fig. 19
shows the true shape intended, but the darker
squares show that the digitized form yields a
non-monotonic left boundary. METAFONT
compensates for this sort of problem by
keeping track of the desired boundaries when
the pen width is varying, plotting points twice
(e.g. plotting both (x, y) and (x-1, y) ) when
necessary to keep the boundary correct. In
other words, the idea of rounding the pen
location and the width independently is some¬
times effectively abandoned.
The final digitization problem that I needed
to resolve was to make the left half of an “O”
look like the mirror image of its right half, to
make a left parenthesis look like the mirror
image of a right parenthesis, and so on. This
was done by having the METAFONT programs
in such cases choose a center point that was
either exactly at an integer or an integer plus Vi,
and to introduce dual rounding which could be
proved to produce exactly the correct
symmetry properties.
ALTERNATIVE APPROACHES
As I have said, I believe the METAFONT
system is successful as a way to define letters
and other symbols, but probably even better
procedures can be devised with further re¬
search. Some of the limitations of my cubic
splines are indicated in Fig. 20. Part (a) of that
illustration shows a five-pointed star and the
word “mathematics” in an approximation to
mathematics
mathematics
mathematics
mathematics
mathematics
■i
i
••***ii
•eattu
Figure 16. Adjusting the letters to
coarser rasters.
Figure 17. Discrete "elliptical" pens of
small integer width and height.
Number 43 Dr. Dobb's Journal of Computer Calisthenics 8i Orthodontia, Box E, Menlo Park, CA 94025 Page 17
100
the optimum curve will have linearly changing
curvature of the form ax + by + c at point
(x, y), and he has suggested choosing the
constants by taking b/a= (y 2 - y 1 )/(x 2 -xj)
between (xj, yi) and (x^, yj), and requiring
that slope and curvature be continuous across
endpoints. Such an approach seems to require
considerably more computation than the cubic
splines recommended here, but it may lead to
better curves, e.g. satisfying the extension-
ality property.
Another interesting approach to curve¬
drawing, which may be expecially useful
for stimulating handwriting, is a “filtering”
method suggested to me recently by Michael
S. Paterson of the University of Warwick (un¬
published). To get a smooth curve passing
through points z^, assuming that these points
my own handwriting, done with straight line writing is inherently un-beautiful, there are still are about equally spaced on the desired curve,
segments so that you can see exactly what the some kinks in Fig. 20(e) that could probably be one simply writes
data points are that I fed to my spline routine, ironed out if a different approach were taken. z(t) = 2(— l)^Z]jf(t—k)/2(—l) k f(t—k)
Part (b) shows the way my handwriting might The most interesting alternative from a k k
look when I get older; it was obtained by mathematical standpoint seems to be tq find a where f(t) is an odd function of order t as
simply setting r=s=2inallthe spline seg- cuive of given length that minimizes the t->0, decreasing rapidly away from zero, e.g.
ments, therefore making clear what tangent integral of the square of the curvature with f(t) = csch t = 2/(e l - e _t ).
angles are prescribed by the system. Part (c) respect to arc length. This integral is propor-
is somewhat more disciplined, it was obtained tional to the strain energy in a mechanical —
by putting r = s = Vi everywhere. Fig. 20(d) is spline (in other words, a thin slat or beam) of
like Fig. 20(c) but drawn with a combined the given length, going through the given
pen-and-eraser. Such a combination can lead points, so it seems to be an appropriate
to interesting effects, and the star here is my quantity to minimize. E. H. Lee and G. E. w
belated contribution to America’s bicentennial. Forsythe [31] have reviewed early work on
When the general formulas for cubic splines this variational problem, and shown that it is
are used as I explained above, we get Fig. 20(e) equivalent to having the spline at equilibrium
in which the star has become a very good with forces applied only at the given points of
approximation to a circle (as I said it would), support. The Norwegian mathematician Evan on
In tliis illustration the pen is thicker and has a Mehlum [36] has shown that if we specify a
slightly oblique stress. Although my hand- fixed arc length between consecutive points,
Figure 18. Difficulties of rounding an arc properly. (Three circles of radius 10 drawn with a 1 x
3 pen.)
Pen width Rounded width
and location and location
(3.5, 0.5,10.5) (3, 0,10) j
(3.7, 0.8, 9.5) (3, 0, 9)
(3.9, 1.1, 8.5) (3, 1, 8)
(4.1, 1.4, 7.5) (4, 0, 7) 1
(4.3, 1.7, 6.5) (4, 1, 6)
(4.5, 2.0, 5.5) (4, 1, 5)
(4.7, 2.3, 4.5) (4, 1, 4)
(4.9, 2.6, 3.5) (4, 2, 3)
(5.1, 2.9, 2.5) (5, 2, 2)
(5.3, 3.2, 1.5) (5, 3, l)
(5.5, 3.5, 0.5) (5, 3, 0)
Figure 20. Examples of the cubic splines ap¬
plied to sloppy handwriting.
I have not had time yet to experiment with
Paterson’s method or to attempt to harness
it for the drawing of letters. It is easy to see
that the derivative z'(zk) = f( l)( z k+t -zk_ j)
- f(2)(zjj +2 -zjj.j) + ... lies approximately
in the direction of zj, +1 - zj c _ 1 .
Figure 19. Failure of monotonicity due to independent rounding. (Rounding takes (w,x,y) into
(Lwj, Lx-S (lwj) ,LYj) •)
Page '18
Dr. Dobb's Journal of Computer Calisthenics 8c Orthodontia, Box E, Menlo Park, CA 94025
Number 43
101
RANDOMIZATION.
BIBLIOGRAPHY.
In conclusion, I’d like to report on a little
experiment that I did with random numbers.
One might complain that the letters I have
designed are too perfect, too much like a
computer, so they lack “character.” In order
to counteract this, I can build a certain amount
of randomness into the choices of where to put
the pen when drawing each letter, and Fig. 21
shows what happens. The coordinates of key
pen positions were chosen independently with
a normal distribution and with increasing
standard deviation, so that the third example
has twice as much standard deviation as the
second, the fourth has three times as much, and
so on. Note that the two m’s on each line
(except the first) are different, and so are the
a’s and the t’s, since each letter is randomly
drawn.
After the deviation gets sufficiently large
the results become somewhat ludicrous; and I
don’t want people to say that I ended this
lecture by making a travesty of mathematics.
So let us conclude by looking at Fig. 22, which
shows what is obtained in various fonts when
the degree of randomness is somewhat
controlled. I think it can be said that the letters
in this final example have a warmth and charm
which makes it hard to believe that they were
really generated by a computer following
strict mathematical rules. Perhaps the reason
the printing of mathematics looked so nice in
the good old days was that the fonts of type
were imperfect and inconsistent.
SUMMARY.
I’d like to summarize now by pointing out
the moral of this long story. My experiences
during the last few months vividly illustrate
the fact that there are plenty of good mathe¬
matical problems still waiting to be solved,
almost everywhere you look-especially in
areas of life where mathematics has rarely been
applied before. Mathematicians can provide
solutions to these problems, receiving a double
payoff-namely the pleasure of working out
the mathematics, together with the apprecia¬
tion of the people who can use the solutions.
So let’s go forth and apply mathematics in
new ways.
ACKNOWLEDGMENTS.
I would like to thank my wife Jill for the
many important suggestions she made to me
during critical stages of this research; also Leo
Guibas and Lyle Ramshaw for the help they
provided in making illustrations at Xerox Palo
Alto Research Laboratories; also Lester
Earnest, Michael Fischer, Frank Liang, Tom
Lyche, Albert Meyer, Michael Paterson, Michael
Plass, Bob Sproull, Jean E. Taylor, and Hans
Wolf, for helpful ideas and stimulating discus¬
sions and correspondence about this topic; also
Gordon L. Walker, for verifying my conjectures
about the printing history of the Transactions
and for providing me with additional back-
mathematics
' . :i r .
mathematics
mathematics
■ I r_ , -i 4--,
mathematics
math emat ics
mathematics
mathematics
mathematics
math emat ice
, ;
mathe/naticp
mathematics
mathematics
Figure21. Increasingly random pen posi¬
tions; 0 = o. i,..., .
mathematics
mathematics
mathematics
mathaiMtiQS
Figure 22. A bit of randomness introduced
into various styles of type.
ground information; also Prof. Dirk Siefkes for
his help in acquiring Figs. 4(c) and 11(c), and
the Berlin Kunstbibliothek for permission to
publish them; and to Andre Jammes for permis¬
sion to publish Figs. 6 and 11(d).
(I have included here several articles not
referenced in the main text, namely a discus¬
sion of publishing at the American Institute
of Physics [37]; some experiments in type¬
setting physics journals with the Bell Labs
system [32], [7]; computer aids for technical
magazine layout and editing together with a
brief proposal for a standard typesetting
language [11]; reports about early computer
programs for character generation and mathe¬
matics composition [23], [30], [34], [35],
[40], [46]; a description of the mathematics
a traditional printer needs to know [9]; three
standard references on the typesetting of
mathematics [14], [47], [50]; some fonts
of type and special characters designed by the
American Math. Society [39]; a recent
approach to mathematical definition of tradi¬
tional type faces based on conic sections [15];
a proposal for a new way to control the spacing
between letters based on somewhat mathe¬
matical principles [28]; and two purely mathe¬
matical papers inspired by typography [13],
[ 21 ].)
1. A. V. Aho, S. C. Johnson, and J. D.
Ullman, “Typesetting by ACM considered
harmful,” Communications of the ACM
18(1975), 740.
2. American Mathematical Society, “Devel¬
opment of the Photon for efficient mathe¬
matical composition,” Final report
May 10, 1965), National Science Founda¬
tion grant G-21913; NTIS number
PB168627.
3. American Mathematical Society, “Devel¬
opment of computer aids for tape-control
of photocomposing machines,” Report
No. 2 (July 1967), “Extensions of the
system of preparing a computer-processed
tape to include the setting of multiple line
equations,” National Science Foundation
grant GN-533; NTIS number PB175939.
4. American Mathematical Society, “Devel¬
opment of computer aids for tape-control
of photocomposing machines,” Final
report. Section B (August 1968), “A
system for computer-processed tape
composition to include the setting of
multiple line equations,” National Science
Foundation grant GN-533; NTIS number
PB179418.
5. American Mathematical Society, “Devel¬
opment of computer aids for tape-control
of photocomposing machines,” Final
report, Section C (January 1969), “Im¬
plementation, hardware, and other sys¬
tems,” National Science Foundation grant
GN-533;NTIS number PB182088.
6. American Mathematical Society, “To
complete the study of computer aids for
tape-control of composing machines by
developing an operating system,” Final
report, no. AMATHS-CAIDS-71-0 (April
1971), National Science Foundation grant
GN-690; NTIS number PB200892.
7. American Physical Society, “APS tests
computer system for publishing opera-
Number 43
102
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 19
tions,” Physics Today 30, 12 (December
1977), 75.
8. Donald M. Anderson, “Cresci and his
capital alphabets,” Visible Language 4
(1971), 331-352.
9. J. Woodard Auble, Arithmetic for Printers,
second edition (Peoria, Ill.: Bennett,
1954).
10. Michael P. Barnett, Computer Type¬
setting: Experiments and Prospects (Cam¬
bridge, Mass.: M.I.T. Press, 1965).
11. Robert W. Bemer and A. Richard Shriver,
“Integrating computer text processing
with photocomposition,” IEEE Trans, on
Prof. Commun. PC-16 (1973), 92-96.
This article is reprinted with another type¬
face and page layout in Robert W. Bemer,
“The role of a computer in the publication
of a primary journal,” Proc. IFIPS Nat.
Comput. Conf. 42, Part II (1973), M16-
M20.
12. Peter J. Boehm, “Software and hardware
considerations for a technical typesetting
system,” IEEE Trans, on Prof. Commun.
PC-19 (1976), 15-19.
13. J. A. Bondy, “The ‘graph theory’ of the
Greek alphabet,” Graph Theory and Ap¬
plications, Y. Alavi et al., eds. (Berlin:
Springer, 1972), 43-54.
14. Theodore William Chaundy, Percy Regi¬
nald Barrett, and Charles Batey, The
Printing of Mathematics (Oxford: Oxford
University Press, 1954).
15. P. J. M. Coueignoux, “Generation of
Roman Printed Fonts,” Ph.D. thesis,
Dept, of Electrical Engineering, Mass. Inst,
of Technology (June, 1975).
16. Giovanni Francesco Cresci Milanese,
Essemplare de Piv Sorti Lettere (Rome,
1560). Also edited and translated by
Arthur Sidney Osley (London, 1968).
17. T. L. DeVinne, The Practice of Typog¬
raphy: Modem Methods of Book Compo¬
sition (New York: Oswald, 1914).
18. Albrecht Durer, Underweysung der Mes-
sung mit dem Zirckel und Richtscheyt
(Nuremberg, 1525). An English transla¬
tion of the section on alphabets has been
published as Albrecht Durer, Of the Just
Shaping of Letters, R. T. Nichol, trans.
(Dover, 1965).
19. Felice Feliciano Veronese, Alphabetum
Romanum, Giovanni Mardersteig, ed.
(Verona: Editiones Officinae Bodoni,
I960).
20. Frederic W. Goudy, Typologia: Studies in
Type Design and Type Making with Com¬
ments on the Invention of Typography,
the First Types, Legibility and Fine
Hinting (Berkeley, Calif.: Univ. of Cali¬
fornia Press, 1940).
21. F. Harary, “Typographs,” Visible Lan¬
guage 7 (1973), 199-208.
22. Roar Hauglid, Randi Asker, Helen Engel-
stad, and Gunvor Traetteberg, Native Art
of Norway (Oslo: Dreyer, 1965).
23. A. V. Hershey, “Caligraphy for com¬
puters,” NWL Report No. 2101 (Dahlgren,
Va.: U.S. Naval Weapons Laboratory,
August 1967); NTIS number AD662398.
24. Andre Jammes, La Reforme de la Typog¬
raphy Royale sous Louis XIV (Paris:
Paul Jammes, 1961).
25. Paul E. Justus, ‘There is more to type¬
setting than setting type,” IEEE Trans,
on Prof Commun. PC-15 (1972), 13-16.
26. Alan C. Kay, “Microelectronics and the
personal computer,” Scientific American
237, 3 (September 1977), 230-244.
27 Brian W. Kemighan and Lorinda L.
Cherry, “A system for typesetting mathe¬
matics,” Communications of the ACM 18
(1975), 151-157.
28. David Kindersley, Optical Letter Spacing
for New Printing Systems (London:
Wynkyn de Worde Society, 1976).
29. Donald E. Knuth, ‘Tau Epsilon Chi, a sys¬
tem for technical text,” manuscript in
preparation.
30. Dorothy K. Korbuly, “A new approach to
coding displayed mathematics for photo¬
composition,” IEEE Trans, on Prof
Commun. PC-18 (1975), 283-287.
31. E. H. Lee and G. E. Forsythe, “Varia¬
tional study of nonlinear splines,” SIAM
Review 15 (1973), 120-133.
32. M. E. Lesk and B. W. Kemighan, “Com¬
puter typesetting of technical journals on
UNIX,” Computing Science Tech. Report
44, (Murray Hill, N.J.: Bell Laboratories,
June, 1976).
33. Giovanni Mardersteig, The Alphabet of
Francesco Tomiello (1517) da Novara
(Verona: Officina Bodoni, 1971).
34. M. V. Mathews and Joan E. Miller, “Com¬
puter editing, typesetting, and image
generation,” Proc. AFIPS Fall Joint
Computer Conf. 27 (1965), 389-398.
35. M. V. Mathews, Carol Lochbaum, and
Judith A. Moss, ‘Three fonts of com¬
puter drawn letters,” Communications of
the ACM 10 (1967), 627-630.
36. Even Mehlum, “Nonlinear Splines,” in
Computer Aided Geometric Design,
Robert E. Barnhill and Richard F. Riesen-
feld, eds. (New York: Academic Press,
1974), 173-207.
37. A. W. Kenneth Metzner, “Multiple use and
other benefits of computerized pub¬
lishing,” IEEE Trans, on Prof. Commun.
PC-18 (1975), 274-278.
38. Joseph Moxon, Regulae Trium Ordinum
Literarum Typographicarum, or the Rules
of the Three Orders of Print Letters: viz.
the l Roman, ltalick, English | Capitals and
Small; Shewing how they are compounded
of Geometrick Figures, and mostly made
by Rule and Compass (London, Joseph
Moxon, 1676).
39. Phoebe J. Murdock, “New alphabets and
symbols for typesetting mathematics,”
Scholarly Publishing 8 (1976), 44-53.
Reprinted in Notices Amer. Math. Soc.
24(1977), 63-67.
40. Nicholas Negroponte, “Raster scan ap¬
proaches to computer graphics,” Com¬
puters and Graphics 2 (1977), 179-193.
41. Wolfgang A. Ocker, “A program to hy¬
phenate English words,” IEEE Trans, on
Prof Commun. PC-18 (1975), 78-84.
42. Luca Pacioli, Divina Proportione, Opera a
tutti glingegni perspicaci e curiosi neces-
saria Ove ciascun studioso di Philosophia,
Prospectiva, Pictura, Sculptura: Architec¬
ture: Musice: altre Mathematice: suavis-
sima: sottile: e admirabile et doctrina
consequira: e delectarassi: con varie
questione de secretissima scientia (Venice,
1509).
43. Giovanbattista Palatino Cittadino Ro¬
mano, Libro Primo del le Lettere Maiu-
scole Antiche Romane (unpublished),
Berlin Kunstbibliothek MS. OS5280.
Some of the individual pages are dated
1543, 1546, 1549, 1574, or 1575. See
James Wardrop, “Civis Romanus Sum:
Giovanbattista Palatino and his circle,”
Signature, n.s. 14 (1952), 3-39.
44. Paul A. Parisi, “Composition innovations
of the American Society of Civil Engi¬
neers,” IEES Trans, on Prof Commun.
PC-18 (1975), 244-273.
45. R. G. D. Richardson, ‘The twenty-ninth
annual meeting of the Society,” Amer.
Math. Soc. Bulletin 29 (1923), 97-116.
(See also vol. 28 (1922) pp. 234-235,
378 for comments on the special Trans¬
actions volume, and pp. 2-3 of vol. 28
for discussion of deficits due to increased
cost of printing.)
46. Glenn E. Roudabush, Charles R. T. Bacon,
R. Brace Briggs, James A. Fierst, Dale W.
Isner, and Hiroshi A. Noguni, ‘The left
hand of scholarship: Computer experi¬
ments with recorded text as a communica¬
tion media,” Proc. AFIPS Fall Joint
Computer Conf. 27 (1965), 399-411.
47. Ellen E. Swanson, Mathematics Into Type
(Providence, R.I.: Amer. Math. Soc.,
1971).
48. Francesco Tomiello, Opera del Modo de
Fare le Littere Mauiscole Antique (Milan,
1517).
49. Geofroy Tory, Champ Fleury (Paris,
1529). Also translated into English and
annotated by George B. Ives (New York:
GrolierClub, 1927).
50. Karel Wick, Rules for typesetting mathe¬
matics, Tr. by V. Boublik and M. Hejlova
(The Hague: Mouton, 1965).
51. Hermann Zapf, About Alphabets: Some
Marginal Notes on Type Design (Cam¬
bridge, Mass.: M.I.T. Press, 1970).
Page 20
Dr. Dobb's Journal of Computer Calisthenics 8< Orthodontia, Box E, Menlo Park, CA 94025
Number 43
103
QYHVIROT * Generating Symbol Table
3I1UDUL. Alpha Listing on the Hg
BY WILLIAM W. MOSS accessory data can follow each element of the string table
1507 Riverview Lane without affecting the sorting. In this program the symbol’s
Bradenton, FL 33505 value follows the string itself. There is no software limit to
the number of strings which can be sorted, as all variable in
the sort routine are 16-bit values, and thus the real limitation
Enclosed is a listing of the program ‘SYMBOL’ which is the addressing space of the hardware (65 kilobytes). The
generates alphabetically sorted listings of the symbol table limit for the number of bytes which can be compared from
from runs of the Heath H8 assembler. To utilize the program each string is 255 since one byte is allowed for this rvalue,
one simply has to rim it immediately after a run of the as- The initialization requirements are given in the listing of the
sembler (i.e., before another program writes over the assembler routine. At the end of the sort the table containing the pointer
symbol table in memory). The table is then printed out in addresses to the string data has been rearranged such that the
column order on the console. The symbol values are listed in first address is the pointer to the first alphabetically ranked
offset octal format. Hexadecimal format can also be used if string, etc., down to the alphabetically lowest string,
desired by substituting the routine ‘HEXOUT’ for ‘OCTOUT’ The program is written with standard Intel 8080 assembly
and changing the code in the ‘PRINT’ routine as shown in the language mnemonics except for the use of four Heath DOS
accompanying listing. calls (SCALL) which are defined as follows:
Of general interest to Intel 8080 or Zilog Z80 users is
the inclusion of a routine (SMSORT) which performs the (1) .SETTOP sets upper memory limit in HDOS.
alphabetical sorting of variable length character strings utiliz- (2) .SCOUT outputs the character in register ‘A’ to con¬
ing the efficient Shell-Metzner algorithm. The speed of this sole.
routine is further increased because the strings in the data (3) .ERROR prints out system error messages,
table are not physically swapped during the sort: 2-byte (4) .EXIT returns to system monitor,
pointers are exchanged instead. Because the string data table
is unchanged and only the number of characters specified As an example of the program’s output the symbol table
in the length byte are actually compared for sorting purposes, for the program itself is listed.
ASM
HDOS AS*-eML»ler Issue ♦104*02.OO.
*. -SYMBOL
00353 Strttemerit* Assembler!
11924 Buies Free
No Errors fie Lee ted
sm»o!
ERROR 000 O '57 FRRUR 044 044 READLBL 042.233 TABADDR 043.214
, F >' I r 00O 000 I. Bl TAB 044.110 ROWCNT 043.251 USEC 043.040
.SCOUT 000,002 NEWI.RL 04' 31 S.OMAY 040.324 USERFUA 042.200
.SETTOR 000 052 NFWI J NF 043.24? SFTI 043.014 VAR T 044.0*4
ALL DONE 044 07" NFXTIBl 042.310 SET 1 043.14? OARJ 044.074
ASMTAB 075,134 NOMATCH "4^ 101 SFTL 043.02? VARK 044.100
COLUMNS 000.004 Or TOUT 044,040 SETM 042.350 VARl 044.10 7
t.OMP 043 0'4? POINT 04 4 SMSORT 042.340 VARM <'44 t"4
i.KI P 000 017 POIMTAB 044.0*2 SPACES 044.027 VARN 044,106
DEMHl. 043.20? PRINT 043.236 STROUT 043.332
BIGOUT 044.04* READCHP 042.2 3'* SYMVAL 043.226
SYMBOL TABI E SORTER AND PRINTER FOR HH ASSEMBLER HEATH ASM 1104.02.00.
M|l! TAM W. MOSS - 1 JUNE. 1979
* PROGRAM TO PRINT OUI AN ALPHABETICALLY SORTED SYMBOL TABLE FOLLOWING USE
* OF THE HEATH H8 ASSEMBLER [VERSION t04.02.00J
*
♦ TO IISFJ ASSEMBLE AS USUAL WITH THE HEATH ASM PROGRAM.
+ IMMEDIATELY AFTER THE ASSEMBLY IS COMPUTED RUN THIS PROGRAM.
♦ THF SYMBOL TABLF IS THEN PRINTED ON THE CONSOLE
♦ definitions:
♦
"0.004 cm UMNS EGU 4 NUMBER OF COLUMNS DESIRED IN TABLE LISTING
075.136 ASMTAB EQll 75136A FWA SYMBOL TABLE FOR ASM 104.02-00
00O.012 CRLF EGU 10 CARRIAGE RETURN / LINE FEED CHARACTER IN HDOS
04".?>4 S.OMAX EGU 40324A SYSTEM OVERLAY MA*IMUM SIZE
"47. USERFUA EGU 42200A START OF USER MEMORY IN HDOS
* HEATH DOS SYSTEM CALL DEFINITIONS:
Number 43
104
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 21
000.052
000.002
000.057
000.000
.SETTOP EGU
•SCOUT EQU
.ERROR EQU
.EXIT EQU
04 ?. 200
042.203
042.205
04.1 377 377
377 052
353
* ROUTINE TO SET MAXIMAL USER HIGH MEMORY LIMIT IN HDOS
LXI Hr-1 REQUEST ALL OF MEMORY (I.E. TOO MUCH)
042.206 052 324 040
042.211 001 012 000
042.214 011
042.215 315 207 043
>4 20 m 052
042.222 332 064 044
S.OMAX
HL
= OVERLAY
SIZE
B. 10
B
HL
= OVERLAY
PLUS MARGIN
FOR ERROR
DEMHL
HL
= MAX MEM
- OVERLAY -
10
.SETTOP REQUEST MEMORY LIMIT
ERROR JUST IN CASE SOMETHING AMISS
* ROUTINE TO MOVE AND RESTRUCTURE THE SYMBOL TABLE
* FINAL STRUCTURE:
* BEGIN AT 'LBLTAB'.
* DATA UNIT FOR EACH SYMBOL t
* (1) LENGTH OF SYMBOL CHARACTER STRING ('N') - 1 BYTE
* (2) STRING DATA - 'N' BYTES
* (3) SYMBOL'S VALUE - 2 BYTES - STORED IN LOW/HIGH FORM
042.225
042.230
042.233
042.234
042.235
042.237
042.240
042.241
042.242
042.245
042.247
042.250
042.251
042.252
042.253
042.254
042.257
042.260
042.261
042.262
042.263
042.264
042.265
042.266
042.267
042.270
042.271
042.272
042.273
041 136 075
021 110 044
325
023
016 000
176
107
247
312 276 042
346 177
022
023
043
014
270
312 237 042
043
176
022
023
043
176
022
023
043
343
161
341
303 233 042
LXI
LXI
READLBL PUSH
INX
MV I
READCHR MOV
MOV
ANA
JZ
ANI
STAX
INX
INX
I NR
CMP
JZ
INX
MOV
STAX
INX
INX
MOV
STAX
INX
INX
XTHL
MOV
POP
JMP
IF END OF TABLE REACHED
CLEAR HIGH BIT
HrASMTAB
DtLBLTAB
D SAVE ADDR FOR STRING BYTE COUNT
D
C»0
ArM
BfA SAVE CHARACTER
A
POINT IF END OF TABLE REACHED
177Q CLEAR HIGH BIT
D
D
H
C
B SEE IF HIGH BIT WAS SET
READCHR
H SKIP CODE BYTE
A » M
D SAVE LOW BYTE
SAVE HIGH BYTE
HI - ADDRESS FOR BYTE COUNT
STORE BYTE COUNT
* ROUTINE TO CONSTRUCT A POINTER TABLE FOR THE STRING DATA TABLE.
* STRUCTURE AS FOLLOWS?
* BEGIN AT < POINTAB').
* EACH TWO BYTF DATA ITEM IS THE ADDRESS OF THE START (JF DATA
* FOR EACH SYMBOL IN THE STRING DATA TABLE.
042.276
341
POINT
POP
H 1
042.277
160
MOV
Mr B 1
042.300
043
INX
H
042.301
042
072
044
SHl.D
F’OINTAB
04?.304
353
XCHG
042.305
041
110
044
LXI
HfLBI TAB
042.310
176
ne:xtlbl
MOV
A.M
042.311
247
ANA
A 1
042.312
312
340
042
JZ
ShSORT
042.315
1 75
MOV
AfL
042.316
022
STAX
D
042.317
023
INX
D
042.320
174
MOV
A.H
042.321
022
STAX
P
042.322
023
INX
t
042.323
00 3
‘iNX
B (
042.3' 4
176
MOV
A.M
042 3 5
306
003
ADI
3 i
042.327
205
ADD
L
04? 330
157
MOV
L. r A
042.331
1 7 4
MOV
ArH
042.332
316
000
AC I
0
042 534
147
MOV
H » A 1
4
303
310
042
JMP
NFXTI BL
HL = (LWA OF LBLT.iB) FI
MARK END OF LBLTAB WITH 0 (DC
END OF LBLTAB?
COUNT LABELS IN TABLE
LENGTH OF LABEL + 3 DATA BYTFS
0 .ON ENTRY'
* SHELL-METZNER STRING SORTING ROUTINE
* ENTRY: BC NUMBER OF STRINGS TO BE SORTED
* ('POINTAB') = START OF POINTER TABLE
* POINTER TABLE MADE UP OF A SERIES OF 16 BIT ADDRESSES
* POINTING TO THE POSITION IN THE DATA TABLE FOB I mCH
+ OF THE ITEMS TO BE SOPTED.
* DATA TABLE STRUCTURE•
* FTRST BYTF = LENGTH OF STRING
* FOI LOWING BYTES - STRING CHARACTERS
* BYTES BEYOND SPECIFIED LENGTH ARE IGNORED
* EXIT? POINTER TABLE REARRANGED TO POINT TO STRINGS IN ALPHABETICAL ORDER.
* STRING DATA TABLE IS UNCHANGED-
* VARN - NUMBER OF STRINGS SORTED.
04? <40
i ma
SHSORT
MOV
042.<41
151
MOV
■•A? 34'’
042
106
044
SHI D
042,345
042
104
044
SHLD
•"'4 2 . 350
05?
.104
044
SFTM
l HL D
. 353
1 74
MOV
04? 354
747
ANA
Page 22
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
105
04°» 355
03 7
RAR
04 2,356
1 47
MOV
Hr A
042.357
175
MOV
ArL.
04 2.360
037
RAR
04''. 5At
157
MOV
L » A
042.362
04?
104
044
SHI D
VARM
VARM - VARM / 2
04? 365
>64
ORA
H
04 j . 3/.A
31?
236
043
JZ
PR INI
IF END OE SORT
042 ! '1
041
001
000
LXI
Hr i
042,574
04' 1
CV7/S
044
SHL 0
VAR J
VARJ - 1
042 177
052
106
044
L HI D
VARN
'•4 5.00:
45 3
XCHG
043 003
052
104
044
LHLD
VAPM
04 S •••■■
315
,'07
043
CA1 I
DEMHL
04 <. 011
04?
100
044
shi, n
VARK
VARK -= VARN - VARM
O 45 •Ot4
05?
0 76
044
SET I
1 HID
VAR 1
043,03 *
04?
r> ? 4
044
SHL D
VAR T
VARI - VARJ
043,0?
05 ?
074
044
SETL
LHLD
VAR 1
043.025
353
XCHG
04 • .026
7>5?
104
044
LHLD
VARM
044 031
'• <1
DAD
D
043.03?
r*4?
102
044
SHLD
“AH
VARL ^ VAR I + VARM
043 035
315
226
043
CALL
SYMVAL
HL = STARI OF DATA POINTED BY VAKI
, lA J ,
345
PUSH
H
043.041
052
074
044
LHLD
VARM
043 044
315
226
043
CALI...
SYMVAL
04 04
3?'
POP
D
04 3.nso
0 32
1 DAY
D
A * CHAR COUNT POP STRING T VAR! 1
04
11.6
MOV
CrM
C = CHAR COUNT FOP STRING TVAR 1 1
04< 052
271
CMP
r
•>4 3 : O', 3
365
PUSH
PSW
'C' SFT IF LENSTRJNG CVAR11 LLN<
• •43.054
32?
060
04 *
JNC
USEC
■ 05
117
MOV
r»A
043.060
043
USEC
INX
H
C = LENGTH OF SHORTER STRING
043.061
023
I NX
n
HL & DE POINT TO SI ART OF LABEL S
04 i 06?
03?
COMP
LDAX
D
043.063
276
CMP
M
COMPARE STRINGS
043.064
302
101
043
JNZ
NOMATCH
TF NO MATCH
043.06 7*
0?3
INX
D
043.070
043
INX
H
04 < 0 /I
015
DCR
C
043.07»
302
062
043
JNZ
COMP
043•075
361
POP
PSW
CHARACTERS THE SAME, SEE IP ONE SI
04 3 . b «*6
303
to?
04 3
IMP
NOMATCH ft
043 10t
341
NOMATCH
POP
H
CLEAR STACK
043.1o»
^ ?•>
162
043
JNC
SE r 1
TF NO REARRANGEMEN1 REQUIRFD
♦ SWITCH THE P
•HNTFR ADDRESS AT (VARI> WITH THA> A( (VAKI
04 < . 1 O'.
052
.. .1
044
LHL D
VAKI
043 ,H0
315
2'6
...1 ^
CALL
TABADDR
043. i 1 \
345
PUSH
H
STACK = POINTER DATA FOR lVART •
04 3 114
052
102
044
LHLD
VARL
04 4 11/
315
216
043
CALL
1ABADDR
HL - FOTNTFP DATA FOR (VARL'
04 3 | >?
321
POP
n
04 3 » ! : 3
03?
LDAX
D
043 124
107
MOV
B»A
043 125
176
MOV
A.M
043.126
02?
STAX
D
044 1?7
1.60
MOV
M • D
04 < 1.30
023
INX
D
• *43 131
043
I NX
H
043.13?
03?
L DAX
n
04 { 133
107
MOV
B, A
043 - 134
176
MOV
A.M
043.135
022
STAX
D
043.1 <6
160
MOV
M.B
* SWITCH COMPI ETED
043 137
05?
074
044
LHID
VAR l
043.142
353
XCHG
043.143
052
104
044
LHLD
VARM
043.146
315
207
043
CALL
DEMHL
043.151
042
074
044
SHLD
VAR I
VARI * VARI - VARM
043.154
053
DCX
H
043.155
174
MOV
A. H
043.156
247
ANA
A
043.157
362
022
043
JP
SETL
IF VARI >= 1
043.162
052
076
044
SET J
LHLD
VARJ
043.165
043
INX
H
043.166
042
076
044
SHLD
VARJ
VARJ = VARJ + 1
043.171
353
XCHG
043.172
052
100
044
LHLD
VARK
043.175
353
XCHG
043.176
315
207
043
CALL
DEMHL
043.201
332
350
042
JC
SETM
IF VARJ > VARK
043.204
303
014
043
JMP
SETI
* DEMHL
— Hl.
DE - HL
*
entry:
HL * DE
= 16 BIT INTEGERS (UNSIGNED)
*
exit:
HL = DE
- HL
*
DE = UNCHANGED
*
'C' SET
IF HL > DE
*
uses:
A»F»H»L
043.207
1 73
DEMHL
MOV
A.E
043 210
225
SUB
L
043.211
157
MOV
Lf A
043.212
.172
MOV
A* 0
043.213
234
SBB
H
043.214
147
MOV
Hr A
043.215
311
RET
a
045.216
045.217
O45.220
045.221
045.224
* TABADDR -- FIND LOCATION OF DATA POINTER IN TABLE
* ENTRY! HL. = INTEGER VALUE < 1 -> N >
* EXIT.' HL = A DDR OF TWO BYTE DATA POINTER ( FOR INPUT VALUE >
* uses: d»e>h»l»f
TABADDR DCX H
DAD H HL = C(ORIGINAL HL) - ID * 2
* exit:
* uses:
TABADDR DCX
DAD
XCHG
044 L.HLD
DAD
POINTAB
D
Number 43
106
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 23
043.225
31 1
RET
U -
* SYMVAl — FIND DATA RELATED TO INPUT INTEGER VALUE IN ARRAY K
%
ENTRY:
HL - INTEGER VALUE < 1 -> N ) POINTING TO DATA ARRAY
*
exit:
HL = FWA STRING DATA FOR THAT VALUE
*
uses:
A r D r E r H r L r F
043.226
315
216
043
SYMVAL
CALL
TABADDR
043.231
176
MOV
ArM
043 232
043
INX
H
043.233
146
MOV
H » M
043.234
157
MOV
l rA
043.235
311
RET
* SORTING IS COMPLETED. NOW PRINT OUT TABLE.
043.236
042
074
044
PRINT
SHLD
VARI VARI 0 (HL - 0 ON EXIT FROM SMSORTJ
043.241
353
XCHG
DE = 0
043.242
001
374
377
l XI
B»-COLUMNS COMPLEMENT OF NUMBER OF COLUMNS
043.245
052
106
044
LHLD
VARN
043.250
053
DCX
H
044 251
01 1
ROWL'NI
DAD
B
('4 4.252
023
INX
D
043. :»r>3
332
251
043
JC
ROWCNT
043.25*
35 i
XCHG
043,257
042
104
044
SHL D
VARM VARM NUMBER OF ROWS TN TABLE
043.262
076
012
NEULINE
MVI
ArCRLF
043.264
377
002
SCALL
.SCOUT CR/LF TO CONSOLE
043.266
076
004
MVI
A»COLUMNS NUMBER OF COLUMNS TO PRINT
043.270
062
100
044
STA
UflRK VARK = NUMBER COLUMNS LEFT TO BE PRINTED
043.273
052
104
044
LHLD
VARM
043.276
353
XCHG
043.277
052
074
044
LHLD
VAR I
043.302
043
INX
H
043.303
042
074
044
SHLD
VARI VARI = LINE COUNT
043.306
042
076
044
SHLD
VARJ VARJ = ARRAY INDEX VALUE
043.311
315
207
043
CALL
DEMHL SUBTRACT VARI FROM VARM
043.314
332
070
044
JC
ALLDONE
043.317
052
076
044
NEWLBL
LHLD
VAR J
043.322
315
226
043
CALL
SYMVAL
043.325
116
MOV
C»M C = BYTE COUNT OF STRING
043.326
076
010
MVI
ft.8 TAB 0 SPACES FOR LABEL VALUES
043.330
221
SUB
c
043.331
107
MOV
B * A B = SPACES NEEDED FOR TAB
043.332
043
STROUT
INX
H
043.333
176
MOV
ArM
043.334
377
002
SCALL
.SCOUT
043.336
015
DCR
C
043.337
302
332
043
JNZ
STROUT
043.342
315
027
044
CALL
SPACED
043.345
043
INX
H
043.346
043
INX
H
043.347
315
040
044
CALL
OCTOUT PRINT HIGH BYTE
043.352
076
056
MVI
Ar ' .
043.354
377
002
SCALL
.SCOUT
043.356
053
DCX
H
043.357
315
040
044
CALL
OCTOUT PRINT LOW BYTE
043.362
041
100
044
LX I
HrVARK
043.365
065
DCR
M
043.366
312
262
043
JZ
NEWLINE
043.371
052
076
044
LHLD
VAR J
043.374
353
XCHG
043.375
052
104
044
LHLD
VARM
044.000
031
DAD
D
044.001
042
076
044
SHLD
VAR)
044.004
353
XCHG
044.005
052
106
044
LHLD
VARN
044.010
353
XCHG
044.011
315
207
043
CALL
DEMHL OUTSIDE ARRAY BOUN‘6?
044.014
332
262
043
JC
NEWLINE YES'
044.017
006
004
MVI
B.4
044.021
315
027
044
CALL
SPACED 4 SPACES BETWEEN COLUMNS
044.024
303
317
043
JMP
NEWLBL
* SPACED — PRINT SPACES ON CONSOLE
*
entry:
B - NUMBER OF SPACES TO B c PRINTED
*
uses:
A. B
044.027
076
040
SPACED
MVI
Ar ' '
044.031
377
002
SCALl
.SCOUT
044.033
005
DCR
B
044.034
302
031
044
JNZ
SPACFB+2
044.037
311
RET
* OCTOUT — PRINT OCTAL VALUE OF BYTE AT M
*
entry:
HL = ADDRESS OF BYTE TO BE OUTPUT
♦
exit:
BYTF OUTPUT TN OCTAL TO CO*QLE
*
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A r F r f
044.040
176
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044.041
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ANA
A CLEAR CARRY
044.042
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044.044
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044.045
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044.050
346
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044.063
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044.064
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044.070
377
000
ALLDONE
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* DATA SECTION
044.072
*
POINTAB
DS
2 (continued on page 38)
Pago 24
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
107
ti 9900
FULLY REENTRANT ^
FORMATTER OPERATING
UNDER TIPMX
PART 2
BY NORMAN V. WALTERS
Software Engineer
R&D Department
Fairfield Industries, Inc.
Houston, TX 77042
This is the concluding segment in a two-part series.
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Number 43
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 27
109
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117
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
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Number 43
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 37
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120
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
BY DAVID E. RAESIDE
Department of Radiological Sciences
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma
This computer program will calculate how much initial
capital you will need to financially survive a given number
of retirement years at a given standard of living. Inflation and
a return on invested capital are accounted for. The retirement
income is assumed to be made up of two components: a fixed
component (a fraction of the initial capital) which is not
indexed to the inflation rate and an inflation indexed com¬
ponent (for example, Social Security).
The program is based upon an article by Edward W. Her old
entitled “How Inflation Affects Your Retirement Dollar ”
which appeared in the September, 1979 issue of the IEEE
magazine Spectrum. Since the program is self-instructional,
it is not necessary to know anything about it to use it.
oooooooooooo
S8o88S8S8S5SSSB55SSSoaaooooooS3S8S88aSc3333^oaaS3ooSSSSQSSSSSSSSSSSSSooooooaoDoS8SSSoS88
Number 43
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 39
121
A HEX KEYBOARD ,
• • WITH APPLICATIONS .
* FOR THE 1802 ELF
BY MARTIN BRONSTEIN
9925 Zelzah #518
Northridge, CA 91325
Martin Bromtein is a 22-year-old senior at California
State University at Northridge, majoring in chemistry. His
interest in computers began when he took a programming class
at school. He was inspired to write this article by Paul Vasser¬
man’s floating point mathpack which appeared in DDJ #37.
Introduction
Loading programs via a microcomputer’s front panel
toggle switches is a cumbersome process to say the least.
The obvious alternative is to use a keyboard. The keyboard
system presented here provides eight bits of hexadecimal
data and uses CMOS integrated circuits for low power con¬
sumption. Software loader programs are not needed to use
this keyboard. Best of all, the system can be built for less
than twenty dollars.
Circuit Description
The heart of this keyboard system is IC 1, National Semi¬
conductor’s 74C922 sixteen key encoder. Input to the encoder
comes from sixteen pushbutton switches arranged in column-
row format.
Pressing any key causes pin 12 on IC 1 to go high. Providing
that the KEYBOARD ENABLE line is high, the signal at
pin 12 is inverted via IC 3a and validates the decoded output
lines of IC 1 through pin 13. The signal at pin 12 is simulta¬
neously sent through R1 and C3, which provide a 1 micro¬
second delay, to pin 3 of flip-flop IC 4. The Q output line
is clocked low to high and this transition is used to clock the
encoder outputs into IC 5, which is used as a quad latch.
The 1 microsecond delay is necessary to insure the outputs
of IC 1 are valid before IC 5 is clocked.
Pressing a second key initiates the same sequence of events
as above, except this time the Q line of IC 4 is clocked low to
high and causes the encoder outputs to be clocked into latch
IC 6. Thus any two consecutive keystrokes causes eight bits
of hexadecimal data to appear on the data lines D4-D7 (MSB)
and D0-D3 (LSB).
After the second key is pressed, a low to high transition
appears on the DATA RDY line which can be used to clock
the data into memory. Only when KEYBOARD ENABLE is
high will keystrokes intitiate the clock signals. The OUTPUT
ENABLE line must be high to allow the data from latches IC 5
and IC 6 to appear on the bus. Operating the CLEAR push¬
button resets flip-flop IC 4 and clears latches IC 5 and IC 6.
CLEAR may be pressed before or after any two keystrokes
to clear the keyboard. If pressed after the first keystroke
in order to correct an error, the DATA RDY line will clock
low to high as IC 4 resets, which may cause problems. /Mi
example of how to handle this situation appears later on in
the section on interfacing the keyboard to the 1802 Elf.
Construction
Any type of construction may be used, such as vector
board or printed circuit. IC sockets are advisable since CMOS
ICs are sensitive to static discharges and should not be placed
in the circuit until all soldering is complete.
A suitable keypad may be made from sixteen individual
momentary-contact pushbutton switches. Complete hex
keypads are available from various mailorder dealers such as
Jameco Electronics (1021 Howard Ave., San Carlos, CA
94020) for about eleven dollars.
A very inexpensive alternative is to use a surplus calculator
keypad. The basic four function (+, —, X, -r) type is best.
These keypads are usually wired in colum-row format already
and can be bought as surplus for about 1 dollar. One place
that has them is Computer Components Inc. (5848 Sepulveda
Blvd., Van Nuys, CA 91411). The keytops can be marked
with the appropriate numbers and letters using white tape
and a marking pen.
Page 40
122
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
Interfacing the Elf 1802
The hex keyboard may be interfaced to the original Elf
with two simple modifications.
First, locate the junction of pin 10, on IC 11, and the
cathode of D5. Break the junction connection to pin 11 of IC
12 (see fig. 2) and insert the circuit shown in fig. 3. The new
circuit allows the keyboard DATA RDY signal to clock the
data on the bus into memory in the same manner as depressing
the INPUT switch on the Elf.
The second modification involves locating the connection
from pin 2 of IC 11 to pins 5, 6, 12, and 13 of 1C 8 and 9
on the Elf. Break this connection and insert a DPDT toggle
switch as shown in fig. 4. This switch is used to select opera¬
tion of either the keyboard or the Elf’s original toggle
switches. This is necessary in order to prevent the toggle
switch’s data from reaching the bus while using the keyboard
and vice versa. All other connections remain intact.
Finally, connect the KEYBOARD ENABLE line to the
N2/LOAD line on the Elf (pin 1 of IC 10 will do) and connect
RESET to pin 10 of 1C 12 on the original Elf. The bus connec¬
tions may be made directly to the microprocessor. All of the
interface connections are summarized in figure 5.
The keyboard can now be used to program the Elf. Set
the selector switch for keyboard operation, set the Elf LOAD
switch to ON and press any two keys. The data will auto¬
matically appear on the display and be loaded into memory.
All the Elf operating procedures remain the same.
PARTS LIST
R1 - 10K y 4 W resistor, 10%
R2 - 22K y 4 K resistor, 10%
Cl — 1 mfd 10V. electrolytic capacitor
C2 — 0.1 mfd mylar or disk capacitor
C3 — 100 pf disk capacitor
IC1 - 74C922 16 key encoder
IC 2,7,8 - 4066 quad analog switch
IC — 34049 hex inverter
IC4 - 4013 dual D flip-flop
IC 5,6 — 74C175 quad latch
IC 9 — 4023 triple 3 -input NAND gate
SW 1 — momentary contact push button switch
D1 — 19914 switching diode
Misc. — hexadecimal keypad, vector board, etc.
Page 42
124
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
KUDOS FOR JANUARY ISSUE
Dear Suzanne:
WOW! SUPER! EXTRAORDINARY! GREAT!
There are just not enough adjectives available to convey my
impression of the January 1980 issue.
I’m sick of TRS-80, PET, APPLE, ATARI, etc. Why do
they get all the play when the only true universal operating
system around is CP/M? There must be 1000 mentions of
TRS-80 to each mention of CP/M in the micro-computer
press.
So you can well imagine how happy I was with your
latest issue.
Only one request: PLEASE GIVE US LOTS MORE CP/M!
Thank you, Gramer & Company
E. E. (Bud) Gramer P.O.Box 35336
Phoenix, AZ 85069
Dear Ms. Rodriguez:
The all-CPM issue was excellent (of course!) and those of
us who march to different beats will hope for an all-DOS issue
or whatever. I have one small nit to pick. In your lead editorial
you state: “Since CP/M is the most popular micro operating
system in the world ...” but is it really? Radio Shack pumps
out a hundred thousand or so units each year and more and
more of these are diskette based. So their DOS might well be
the champ in terms of total use. If CP/M is the winner it must
be by the combination of industrial and hobby market sales.
Our business (which is also our hobby, our crusade, our
religion etc.) is plagued with these funny blind spots.
Dr. Dobb’s sometimes acts as if Radio Shack doesn’t exist.
Most writers on programming subjects ignore the very
existence of RPG. PASCAL is praised as “structured” and
COBOL condemned as “unstructured,” and never mind the
fact that top-down programming is easy in the latter and
impossible in the former. By no means do I expect everyone
or even a majority to share my particular likes and dislikes,
but equal time would be fairer and would in fact make for
some interesting debates.
So let’s hear it for all the unloved ones in the land of the
bit and the byte. Three cheers for Radio Shack, hurrah for
COBOL, and de facto recognition at least for poor old RPG.
Even a respectful bow to big bad IBM (or did you think I
was using a Heathkit typewriter?)
Cheers, Culleton Group
John R. Culleton, Jr. 2401 Haight Avenue
Sykesville, MD 21784
NEWBERRY ADDENDUMS
Dear Editor:
Some corrections to my article “An Overview of CP/M
Compatible Software” in DDJ #41.
Page 9, column 1, middle of page, two occurrences of the
name ‘Sam Singer’ are misspelled as ‘Sam Sinser.’ Page 11,
column 1, top of page, line 4, change “‘bmfMVI C, IZOtt:
(or ‘bmfMVI C,l’)” to “‘bmfMVI C, UZOtt ’ (or ‘bmfMVI
C,lAZOtt.)”
Page 13, column 1, top of page, PASCAL/Z: I have since
obtained the up-to-date documenation of PASCAL/Z
(Version 2) which now has REALs (floating point) and point¬
ers, and so is a full spec PASCAL except for the omission of
variant records and the ability to pass procedures and func¬
tions as parameters.
Finally, I entirely omitted any mention of the TDL/Xitan
line of software because of the collapse of the company. I have
since learned that a new firm (Computer Design Labs, 342
Columbus Avenue, Trenton, N.J. 08629) has been formed to
maintain and distribute the TDL/Xitan line. Available on
either 5or 8" disks for standard CP/M, North Star CP/M
and TRS-80 CP/M, the line requires a Z-80 processor. I par¬
ticularly recommend the ZTEL, MACRO II, LINKER and
ZAPPLE packages as outstanding values.
Cordially, Newberry Microsystems
Steve Newberry 24225 Summerhill Ave.
Los Altos, CA 94022
POLYMORPHIC 8813 MATH FUNCTIONS
Dear Suzanne,
I use a Polymorphic 8813 as a home system (and sometimes
think I am the only person in the world to own one). As a
precision buff, I was delighted by their newest release of
BASIC which among the many other features, has variable
precision “settable” from 6 to 26 digits. By the way, this
precision holds for all of the trigonometric and other math
functions unlike the so-called double precision calculations in
some other BASICs.
While playing with some mathematical diversions based on
repeating fractions, I found a need to do some simple arith¬
metic with even greater precision that that already offered.
After an hour or so of playing around with the disassembler, I
found a patch to allow a limited amount of calculation to be
done in precisions up to 62 digits.
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 43
125
The following code appears in the system overlay
“Bdir.OV”. A simple change of one byte on a COPY of the
overlay using the “Szap” utility on the System Programmer’s
disc allows the increased precision.
;The following code resides at 2395H in the overlay area.
CD XX XX
CALL
PARAM
;get number
7B
MOV
A, E
;get returned byte
FE 06
CPI
06H
; see if too small
OE 32
MVI
C, 32H
;get small error code
DA XX XX
JC
ERROR
; 3FE5H is error location
FE IB
CPI
1BH
; test for too large
;The preceeding two bytes must be changed to “FE 3F” for
; increased precision operation.
OE 33
MVI
C, 33H
; large error code
D2XXXX
JNC
ERROR
; do error
;etc, etc,.
It should be noted that the math functions are not guaranteed
to work well at the increased precision, in fact the trig
functions will never be better than 26 digit because the con¬
stants built into the algorithms are not precise enough. The
“Emedit” utility can be used to change the error message
relating to precision limits as desired. The following operations
have been used with success at 62 digits:
+, *, /, INPUT, PRINT, PRINTrn, SQRT, ABS,
SGN, DO-loops and comparisons.
Hope this may be of help to some other hackers out there.
Sincerely, 23 Mack Drive
John W. McGaw Las Vegas, NV 89110
INVISIBLE PROGRAMMER S LAW
Dear Suzanne:
This letter is in reference to my article in DDJ #40, “An
Interactive Heath H-8 Disassembler.”
I would like to correct two errors in the article, one in the
text and the other in the program listing.
In the 9th line from the end of the text (before the pro¬
gram listing), change the word “command” to “comment.”
My meaning here was to delete the text from the REM state¬
ment, but leave the REM.
In the program listing, line 3010 has a GOTO referencing
a non-existent line 3150. This line was inadvertently omitted.
Therefore, insert the following two lines:
3150 REM 01110110 ‘HLT’ INSTRUCTION
3160 S$ = “HLT” : GOSUB 6000: RETURN
These lines are necessary for the disassembly of HLT
commands. Their omission causes no problem until such a
command is encountered. Although I had tested this program
many times before submitting it, I apparently had not dis¬
assembled any programs using the HLT command until
after I had mailed the program to you. I am now convinced
of the programmer’s law which states that every program
contains at least one bug that is totally invisible to the pro¬
grammer until after the program is published, at which time
the bug will be immediately obvious to even the most casual
observer.
I received a question about line 5530 which may have
bothered someone else. The inquiry was whether the argu¬
ment of CHR$(c) was a “c” or an “o.” This character is a
“c” and is the same “c” referred to in line 5510.
I now have a question. Do you know of any policy on
rights to programs which have been converted from one
machine to another, where the revision may be extensive
(up to 50%), but some of the original good ideas have been
kept? For example, I have converted several machine code
programs written for the TRS-80 to run on my Heath H-8.
Since the CPU chips are different and the architecture is quite
different, the programs required substantial revision. I would
like to publish these (especially a useful Monitor/Debugger)
for use by other H-8 owners, since software is not so readily
available for this machine. However, I don’t want to infringe
on any copyrights or get into any legal problems. I would
appreciate any advice from you or your readers on this.
Thanks for the good job you’re doing with Dr. Dobb’s.
Sincerely, 3822 Murworth Drive
Ronald T. Borochoff Houston, Texas 77025
The following mini program was sent to us by Holger
Petersen of West Germany, whose Z80 Micro Disassembler
was published in DDJ #38.
HOW TO CHESS-MATE MICROCHESS!
Dear Suzanne:
I send you this chess note to form a system-tape.
First step : Have a 16K level II TRS-80
second step : Have a Microchess-tape and T-BUG
third step : Load T-BUG, and with the T-BUG :
fourth step : Load the first take of MICROCHESS
fifth step : Change the following locations
4FB3 from
40 to
60
4FCA
4F
6F
4FD9
C2
00
4FdE
3C
70
4FE5
40
74
4FEA
CD
48 01 to
C3 XX YY (jump to your T-I -
sixth step :
Load the second take of MICROCHESS by juinpmg
from T-BUG to 4FA4!
seventh :
Insert a short program at 6000 :
6000
21
CO 60
LDHL
6003
11
CO 40
LDDE
6006
01
00 10
LD BC
6009
ED
BO
LDIR
600B
21
00 70
LDHL
600E
11
00 3C
LD DE
6011
01
00 04
LD BC
6014
ED
BO
LDIR
6016
C3
FD 41
JUMP microchess microchess
eighth step :
Save all from
6000 to 73FF on a tape!
Start address is 6000!
ninth step: Try it out!
To note : And how wild you disguise your software, the first part of
it must come into the machine the normal, vulnerable way!
Number 43
126
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Paige 45
UCSD PASCAL WITH DIGITAL SYSTEMS DDOS
Dear DDJ:
After our club made a group purchase of UCSD PASCAL
over a year ago, I was anxious to try it out. I had enough
memory, 48K, a Digital Systems (now Digital Microsystems)
double density floppy disk, and CP/M 1.4, modified by Digital
Systems to work with either double or single density.
Tire PASCAL was set up for single density, so following the
instructions from Digital Systems, I constructed a single den¬
sity operating system. It worked just as it was supposed to on
regular CP/M files, and I was able to get into PASCAL and set
it up to work with my terminal.
However, I soon became very frustrated. I could copy a
complete PASCAL disk; I could change the date—which gets
written to the disk; but I could not save a workfile or copy a
file from one disk to another.
After trying all kinds of things with many suggestions from
local club members, I despaired of getting PASCAL on my
system. However, I eventually got a lead to Bruce Sherry in
California, who had worked on Digital Systems software. He
provided helpful suggestions that led to the solution of the
problem.
The difficulty arises in the CP/M BIOS. Because the version
from Digital Systems can handle single density in one drive
and double density in another, a table in the BDOS has to
be modified depending upon which density is in effect at
a given time. This is done by the SELDSK routine in the BIOS.
Unfortunately, PASCAL uses the area normally occupied
by the CP/M BDOS, so when SELDSK modifies BDOS, it is
actually modifying part of the PASCAL operating system. As
long as one is going to use PASCAL only in single density
mode;, there is no need for SELDSK to modify BDOS.
Tire cure is easy: simply eliminate a few lines from
SELDSK, recompile BIOS and patch it into CP/M in the
normal manner. If you are starting from scratch to make a
single density operating system, don’t forget to recompile
BOOT so that the system comes up in single density.
Here, in condensed form, are the original routine and the
modification. In the Digital Systems CBIOS version 4.1
listing, it is located just a few lines below the statement:
“ ; I/O DRIVERS FOR THE DISK FOLLOW”.
SELDSK: :
:SELECT DISK GIVEN BY -REGISTER C
XRA
A
GETDR:
SETSING:
LXT
D.SINGTAB
JMP
0VERB0TH <- Dslete this lin° and all following
SETDOB:
down through "* * 11 cure * * *"
OVERROTH
PUSH
B
LXT
H.BD0S+0FH <- This is tho slue to fch® trouble!
LP10:
POP
B
* * * our*' * * *
LD«
PORT
ANI
0F0H ;CLEAR OUT OLD DISK SELECT BITS
ORA
C ;PUT TN NEW DISK SELECT BITS
ST A
RET
PORT
The routine can be shortened even more, but I would gain
nothing from saving the few bytes involved. After this has
been tested to your satisfaction, you can construct the single
disk boot that will take you straight into PASCAL following
the UCSD instructions.
If anyone gets PASCAL going with Digital Microsystems
double density software, I would be very pleased to hear about
it.
Yours truly, 381 Poplar St.
Charles F. Douds, Ph.D. Winnetka, IL 60093
PET TAPE CUrE
Dear DDJ:
As any PET user knows the most annoying part of loading
from Cassette is waiting for the FOUND ‘ ’ message.
This is mainly due to the lack of a tape counter, but even
with a counter you would not know if the PET has passed the
Program Header. You can sometimes miss the header, wait
several minutes, only to find you are on blank tape. My
method is as follows:
Connect a Soundbox to the user Port Pin 6 (Cassette No. 1
Read) The Soundbox connection is Pin M (CB2 Line).
On both SAVE and LOAD you can then hear the
following:
a) The Header Tone, b) The Header Token, c) The Header
‘Title’, d)The Program DATA, e)The ‘Half Way Point’,
f) Second copy of DATA, g) The end of file Token
By using the F .FWD, PLAY and REW keys you can then
locate the header on a multi-program tape, press PLAY, and
wait. If you do not get the message FOUND ‘ ’ at the
Header Title stage, rewind slightly and try again. Using this
method you can CUE the tape to the right position.
Other advantages are that you can also hear:
a) DROPOUTS, b) CROSSTALK, c) NOISE, d) VARIA¬
TION in PITCH due to tight Cassettes, e) The difference
between DATA and PROGRAM tapes.
This is an invaluable aid, and is best implemented by fitting
a small toggle switch to the cover of the user port connector.
i.e. Position 1 SOUND (Pin M)
Position 2 OFF (No Connection)
Position 3 CASSETTE (Pin 6)
With Pin N being the ‘earth’.
For those who like to keep a ‘Working Copy’ of their
programs in addition to the ‘MASTER’ a separate cassette
is an advantage.
I use an Hitachi TRQ 299 which has an automatic level
control (ALC) and a Cue and Review facility. In my case
the ALC gives perfect results on the PET recordings every
time. The Cue and Review facility allows you to fast wind
using Cue to find the ‘nth’ program on the tape.
Position the header using Review and transfer the tape to
your PET Cassette.
Perhaps somebody will devise a method to convert the
PET Cassette to ‘Cue and Review’.
Incidentally, can anybody suggest a method of recovering
data from a Program tape, on which the header and part of
the first copy of DATA has been erased? (Caused by pushing
RECORD instead of PLAY).
Sincerely, 15 Parkway,
R. Cason Sawbridgeworth,
Herts, England
Number 43
127
Page 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Dr. DoBB'S JoURNALof
COMPUTER
^Calisthenics ^ Orthodontia
Running Light Without Overbyte
Number 44 April 1980 Volume 5, Issue 4
A REFERENCE JOURNAL FOR USERS OF HOME COMPUTERS
An Emphasis on Algorithms!
An Introduction to Algorithm Design 5
Jon Louis Bentley
Algorithm: The first in a Monthly Column About Algorithms 44
Dennis Allison
Meta II: A Syntax-Oriented Complier Writing Language 17
D.V. Schorre
A Northstar BASIC Cross-Reference Tool 26
Titus Purdin
Some Useful Subroutines for a Z-80 Assembler 34
John W. Carter
A Fast Fourier Transform for the 8080 39
Robert D. Fusfeld
129
Kn Introduction
to Algorithm Design
BY JON LOUIS BENTLEY
Carnegie-Mellon University
Pittsburgh, PA 15213
© 1979, IEEE Computer Society
“Algorithm design—that’s the field where people talk
about programs and prove theorems about programs in¬
stead of writing and debugging programs.” Statements along
these lines have been uttered by applications programmers
and academicians alike. But there are also some who say,
“No! Proper algorithm design has helped us to save kilobucks
at our installation every month.” Here we will investigate
the field of algorithm design (also know as “analysis of algo¬
rithms” and “concrete computational complexity,” among
other names) and better equip the reader to judge the field
for himself.
I trust that anyone with even the slightest love for mathe¬
matics burning somewhere in his heart (however deeply)
will want to see how mathematical tools can be applied to the
problems of programming. But for the other readers (whose
interest in mathematics was probably squelched in freshman
calculus), I offer the same bait that hooked me on this field.
I trace my interest in the design of efficient algorithms to the
time when I was a business data processing programmer and
had just finished reading an introductory text on data struc¬
tures. A colleague of mine had just had his program can¬
celled— the operators, by counting the turning rate of the
tapes, had estimated that it would take about three hours to
process his one reel of data. The program itself was fairly short
and a quick glance told us that the time was spent in scanning
a 1000-element table. I suggested that instead of scanning
we try a new-fangled technique I had just read about—
binary search. We did, and the modified program processed
the reel of tape in five minutes, and actually spent most of its
time waiting for the tape! Around that time I was also asked
to help another programmer who had already spent a month
producing over a thousand cards of code for a particular pro¬
gram. A simple change in data structure and a few days’ work
allowed us to redo the program in less than two hundred fines
of code. The redone program was faster than the original
would have been, used far less code, and was much easier to
understand. So even if you have no aeasthetic interest in algo¬
rithm design (yet), please read on—the practical benefits
alone are rewarding enough.
Reprinted with permission from Computer, February 1979.
Throughout this article I refer only to the discrete aspects
of algorithm design. I do not address problems in the domain
of numerical analysis, such as stability, truncation error, and
error propagation. Even with this restriction, I include some
matrices, in which almost all elements are zero, and the fast
Fourier transform.
A number of survey papers on discrete algorithm design
have appeared recently. Hopcroft 1 and Taijan 2 both give a
thorough picture of the field. Weide’s survey 3 concentrates on
techniques for analyzing discrete algorithms, and accomplishes
that task expertly. For those who are skeptical of sweeping
surveys, Knuth’s excellent introductions 4 ’ 5 examine a few
problems in detail. And if one is ready to become a serious
student of the field, the standard texts are Aho, Hopcroft, and
Ullman’s one-semester, graduate-level introduction 6 and
Knuth’s first three volumes 7 ' 9 of his proposed seven-volume
definitive work on algorithms. I hope to supplement those
works by providing a broad survey for the novice. For this
reason, I have kept my list of references short; both Taijan
and Weide, cited above, contain excellent bibliographies.
This survey discusses algorithm analysis from three view¬
points. We first examine five problems and some algorithms
for solving them. Having considered these concrete examples,
we next take a systematic tour of the field. We then investigate
some current research directions and conclude with an assess¬
ment of the field’s value to practitioners.
Some problems and fast algorithms
for solving them
The five problems presented here serve as background to
our general discussions of algorithm design. We will not only
give an algorithm for solving each, but will also mention some
real-world situations in which our problems could exist and to
which our algorithms could be applied. We will analyze the
algorithms’ efficiency and discuss what this analysis shows. We
will study the first problem—“subset testing”—in detail aid
then treat the remaining problems at a more superficial level.
Before moving on to our overview of algorithm design, we will
consider what all this attention to efficiency gets us.
Number 44
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Pcige 5
But first let me offer an explanation of our concern with
these examples. The subset testing problem will raise familiar
issues and should cover some old ground for many; it also gives
us a nice illustration of the tremendous time savings we can get
by using proper algorithms. The next example—the substring
searching problem-provides an extremely interesting blend of
theory and practice. The fast Fourier transform-FFT-is the
third example. It is known to many, uses some important
algorithmic techniques, and is eminently practical. Fourth,
we examine a very old problem-matrix multiplication-and
a recent and remarkably counterintuitive solution. We con¬
clude our examination of specific problems by investigating
algorithmic aspects of a public-key cryptosystem. This system
has recently revolutionized the world of cryptography and
promises to have a substantial impact on “secure” computing.
Subset testing. Given a set A of size n and a set B of
size m<n, is B a subset of A? 10 We can state this “subset
testing” problem as a programming exercise: given an array
A|[l:«] and B [ 1 :m] ,both of (say) 32-bit words, is every word
in B also in A? Disguised versions of this problem arise in
many contexts: set A could be an employee master file, set B
a list of weekly transactions, and the problem, a question of
finding whether a master-file record exists for each weekly
transaction. Or A might be a table of real numbers x with an
associated table S containing sine x, B then being a set of x
values at which the sine function is to be evaluated. But even
though this problem does have many such practical
applications, that is not our main motive in examining it here.
Rather, it leads to many of the basic problems in sorting and
searching, and points to interrelationships between those
problems. It also exposes us to some common algorithm design
methods.
We will examine three solutions to this problem. Finding
the running time of each, by counting the number of
comparisons between elements, will enable us to compare the
solutions. The following may also encourage the reader as he
follows the different solutions: our first algorithm will require
over six days of CPU time to solve a sample problem, while
our final algorithm will solve it in four seconds.
Brute force. The simplest way to accomplish this task is to
compare every element in B to each of the elements of A until
either its equal is found or we have examined all of A and
determined that every element of B has no equal in A (in
which case B is not A’s subset); this approach gives a simple,
two-loop program. If B is indeed contained in A, then each
scan for an element that is B’s mate in A takes n/2 compari¬
sons on the average (you have to look halfway down the list).
Since there are m such scans made, the total number of
comparisons made by this program is about m(n/ 2). So if m is
very close to the size of n, then we will make about n 2 /2
comparisons on the average. We won’t try to analyze the
case that B is not a subset of A; to do so we would have to say
exactly how it is not a subset, and that is very dependent on
the particular problem. Although this algorithm is excep¬
tionally simple to understand and to code, its slow running
time might prohibit its use in certain appplications. We will
now turn our attention to a faster algorithm.
Sorting. If you were given a randomly ordered list of phone
numbers B (say a list of phone numbers in a town) and
another randomly ordered list A (say all phone numbers in the
county) and you were, asked to check whether B was a subset
of A (make sure every town phone number is included in the
county Hst), then you might use the brute-force algorithm just
discussed. If, however, you were handed a town phone book
and a county phone book and asked to perform the same task,
then your job would be much easier. Since the two phone
books are already sorted by name, we can just scan through
the two books together, ensuring that the county book
contains all the town names. This of course immediately gives
us another algorithm for subset testing: sort A, sort B, then
sequentially scan through the two, checking for matches.
To analyze the run time of this strategy we observe that the
scan will take about n comparisons, and we heard somewhere
that you can sort a hst of size n in about n log 2 n comparisons,
so the total running time is (n log 2 n) + (m log 2 m) + n com¬
parisons.
We could pull a sorting routine out of thin air, but it is
not much more difficult to describe one called Mergesort. The
basic operation of Mergesort is merging two sorted lists of
numbers, say X and Y, with these lists either stored as arrays
or linked together with pointers. To do this we compare the
first element of X with the first element of Y and give the
smallest as the first element of the new hst, deleting it from its
source. We repeat this remove-the-smallest step until both X
and Y are empty. Since we used one comparison for each step,
if there were a total of m elements in X and Y, we will have
used about m comparisons. We can now use this tool of
Mergesort
EJ0HED0EII0IIE
The above illustrates the operation of Mergesort applied to a
list of eight elements. The top row shows the eight elements in
the order they were presented for sorting. We then view each
successive pair of elements (31 and 14, 15 and 92, etc.) as pairs
of one-element lists and merge those lists—this amounts to
placing the smaller element as the first element in the list of
length two. The second row depicts this result. We now have
four lists, each of length two. As the next step of our algorithm,
we merge the two successive pairs of lists, giving two (sorted)
lists of length four. As the final step of our algorithm, we merge
that pair of lists, resulting in the list of all elements in sorted
order as shown in the bottom row.
This example had three "levels" of merging, each requiring
work proportional to the number of elements in the list. In
sorting an n-element list we will have log 2 t) levels, with work
proportional to n on each level. Careful analysis shows that if /7
is a power of two, we will use exactly nlog 2 r?-n + 1 com¬
parisons. If we assume that in a program implementing this
algorithm each comparison costs approximately one micro¬
second, then we can sort a million elements in approximately
20 seconds. Using the well-known bubble sort for the same
problem could require up to six days. (We can be encouraged by
the fact that bubble sort will only take three days on the aver¬
age-practice saying that with a straight face to your DP
manager!)
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 44
131
merging to Mergesort a set S of n elements. We start by
viewing S as a set of n sorted one-element lists. We then merge
adjacent pairs of one-element lists, giving n/2 two-element
lists. The next step is to merge adjacent pairs of those lists
giving n/4 four-element lists, and the process continues. After
log 2 n iterations we have one sorted n -element list, and our
task is complete. To analyze this we note that we use about n
comparisons for the merges at each of the log 2 n iterations, so
the total number of comparisons used is the promised n log 2 n.
We have thus shown how to solve the subset problem with
n(log 2 n + 1) + m log 2 /n comparisons. If m is about the same
size as n then our algorithm takes approximately 2n log 2 n
comparisons. Can we do better?
Hashing. Thinking about the phone book problem leads to
an interesting sorting approach to the subset problem; if we
rephrase the phone book problem then the “human” approach
will lead to an even faster subset algorithm. Suppose that the
county phone book (A) was sorted and the town phone list
(B) was not; to ensure that A contains B we can “look up” in
A each number in B by the name of the subscriber. For each
of the m elements in B we would do a “binary search” among
the n elements of A. It is not hard to see that a binary search
in an n -element sorted table takes at most log 2 « comparisons,
so this algorithm is easily analyzed: it takes n log 2 w + m log 2 n
comparisons, or approximately 2 n log 2 n if m is the same size
as n. We therefore have a searching solution to the subset
problem: store the elements of A in a table, then for each
element of B ensure that it is in the table.
Although binary search is the best searching method for
many problems, there is another strategy-hashing-even more
appropriate for this problem. By hashing we can store an
element in a table or check to see if it already is in a table in
about two comparisons, on the average. For pessimists,
however, we note that the worst case of hashing is as bad as
brute force—we might have to look at all of the elements in
the table. With this approach we will be able to do subset
testing in In + 2m comparisons -2n to store A and then 2m
to look up each element of B. To store the n elements of A
we will have to allocate a hash table— an array of length
(1.5 )n. We can even use a smaller array; (1.1 )n would probably
work almost as well. We then store the elements of A in the
table one-by-one by the use of a hash function. This maps a
data value into an integer in the bounds of the hash table.
If that position in the hash table is empty, fine. We insert the
element. If the position is occupied, however, we have a
collision and must employ a collision resolution strategy, such
as scanning up the elements of the array until a free position is
found. Analysis shows that a proper collision resolution strate¬
gy allows us to find an empty spot very quickly-say, in two
comparisons. When an empty spot is finally found the element
is inserted. After inserting all of A’s elements into the table we
then look up all of B’s elements. For any particular element
we calculate its hash function and look in that position. If
that position is empty then it is not in A; if the element is
in the position then we have found it; otherwise we must
employ the same collision resolution strategy to see where
it should be. Hashing is something that a human would never
use in searching (humans are much better at comparing things
and then looking in one of two directions than at calculating
weird hash functions), but it leads to a very efficient algo¬
rithm. If m is about the same size as n then the hashing
approach uses only about 4 n comparisons, on the average, to
do subset testing.
The subset testing problem, although a very simple one, led
us straight to some of the fundamental issues in algorithm
design. We very quickly arrived at searching—the scan of the
brute force algorithm was just a naive search. From there we
moved to sorting, then to binary search, and finally to hashing,
which introduced us to a non-obvious data structure—the
hash table. A more thorough examination of searching is
contained in Knuth. 11 The approaches that we used to solve
the problem are some of the fundamental tools of algorithm
designers. We have also touched on aspects of algorithmic
problems such as time and space analysis and worst-case versus
expected-time analysis, which we will study later.
But what has all this gained us? Although we may have a
better understanding of some of the basic computational
issues, does our understanding make any difference in
practice? Let’s assume that we are writing a program for subset
testing where A and B both contain one million elements, and
that one comparison takes, say, one microsecond of computer
time. Under these assumptions, the n 2 /2 comparisons
required by brute force translates to 138 hours, or a little shy
Binary search
This figure shows the operation of binary search in
locating the position of the number 27 in a sorted table. At
the start of binary search we only know that the element, if
in the table at all, lies between 12 and 83, inclusive. This is
denoted by the two "down-arrows" at the top row. We then
compare the middle element of that sequence—41—27. Since
27 is less than 41 we can exclude position 41 to 83 from our
search, denoted by the down-arrows in the second row. Binary
search continues by always examining the middle element of the
sequence in which the "target" value is known to lie. We show
that middle element by an "up-arrow" below it. The binary
search terminates by either finding the desired element or
showing that the desired element is not in the table.
To analyze binary search we note that each time it makes
a comparison the size of the subtable containing the desired
elment is cut by one-half. For example, if we search a 1000-
element table, after one comparison we are down to only 500
elements, after two comparisons to 250, and so on. After about
ten comparisons we either find our man or discover he is not in
the table. In general if there are n elements in the table, binary
search requires approximately log 2 n comparisons. Thus, if we
use it to search a one-million-element table, it will rquire only
20 comparisons, a substantial improvement over the half-million
comparisons used by the average linear scan.
Number 44
132
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 7
of six days, of machine time; the 2n log 2 n for sorting will give
40 seconds; and the 4n of hashing will yield 4 seconds.
Although we haven’t calculated all the costs of implementa¬
tion, this example shows how a simple analysis is sometimes all
we need to make an informed choice.
Substring searching. Does a given string contain a specified
substring pattern, and if so, where? This is the substring
searching problem, one familiar to most who have used
computer text editors. As I sat down to type this paragraph,
for example, I told the editor to find the substring “Substring
searching.” in my text file so I would know where to begin my
paragraph. The text editor I use looks at a file as one long
string of text, sprinkled with special characters representing
“carriage return.” Information retrieval systems use this same
operation as they identify abstracts which contain certain key¬
words. Similar problems are encountered in many text format¬
ting and macro processing programs.
It is not hard to write a program to solve this problem. We
first hold pattern's leftmost character under string’s leftmost
character and start comparing. If all the characters of pattern
match the characters above them, fine—we have found the
substring in position 1. If we find a mismatch then we slide
pattern over one and do the same thing again. This continues
until we either find a match or come to the end of string. The
worst-case behavior of this algorithm is very slow—for each n
positions of string we might have to compare all m positions of
Matrix multiplication
1 “1 x r* n. p
_c dj 1_9 h J Li 1
We can compute a product matrix in the following (non-
straightforward) fashion. First we compute the seven "tem¬
porary" values by the following seven multiplications:
fl ={b-d) * (g+h)
f 2 = (a + rf) * (e + /?)
r3 = (a -c) * (e + f)
f4 = (a + c) • ft
t5 = a * (a - f)
1 6 = d * (g -e)
fl = (c + d) * e
We can now combine these temporary values to yield the pro¬
duct matrix:
p = fl + f2 - f4 + f6
<jr = f4 + f5
r = t6 + r7
S = f2-f3 + f5-r7
The "high school" method of multiplying two-by-two matrices
requires eight multiplications and four additions. This method
requires only seven multiplications, but 18 additions and sub¬
tractions. This hardly seems like a worthwhile tradeoff!
Amazingly enough, however, we can use the above scheme
recursively to oproduce an algorithm for matrix multiplication
that is asympototically more efficient than the 0(r? 3 ) high
2 81
school algorithm—it requires 0(r? ' ) time. Although the sav¬
ings it achieves are offset by the additional overhead in imple¬
mentation (it is probably inferior to the high school algorithm
until the matrix contains at least 10,000 elements), it is remark¬
able to find we can multiply faster than people have been doing
it for the past hundred years.
pattern. Thus in the worst case we might have to make mn
comparisons. Strings and patterns that realize this worst-case
behavior are fairly pathological and the performance of this
algorithm in practice is fairly good, but the question still
haunts us—can we design an algorithm that will always do
better?
Knuth, Morris, and Pratt 12 offer an algorithm that beats
the mn performance. They preprocess pattern into a data
structure that represents a program; that program then looks
for pattern in string. Preprocessing pattern takes only m
operations (where m is the length of pattern) and the
“program” they produce looks at each character of string only
once, so the total running time of their algorithm is propor¬
tional to m + n instead of mn. (Of course if the pattern is in
the tth position in string, then their algorithm takes time
proportional to i + m.) This result is exceptionally interesting
from a theoretical viewpoint, and also provides a faster sub¬
string searching algorithm in practice.
Boyer and Moore 13 recently used the basic idea of the
Knuth, Morris, and Pratt algorithm to derive an even faster
method of substring searching. Their method has the same
worst-case performance (proportional tom + n) but is faster
on the average. They accomplish this by making it unneces¬
sary to examine every element of string. They have
implemented their algorithm on a PDP-10 so efficiently that
when string contains typical English text and pattern is a five
letter word in string, the number of PDP-10 instructions
executed is less than i + n. This is at least an order of
magnitude faster than the naive algorithm.
The history of the substring searching problem provides an
insight into the relation of theory to practice. Knuth relates
that his use of a machine from automata theory, the “two-
way deterministic push-down automaton,” led him to his
discovery of the algorithm. The easiest way to understand fast
algorithms is through the use of finite state automata, which
are commonly used in digital systems design. It is noteworthy
that in this one problem we can talk about such diverse ideas
as abstract automata and PDP-10 instructions, with a lot of
combinatorial analysis in between!
The fast Fourier transform. The Fourier transform is often
studied in mathematics and engineering. It can be viewed in
a number of ways, such as the transformation of a function
from the “time domain” into the “frequency domain” or as
the decomposition of a function into its “sinusoidal
components.” The continuous Fourier transform has a discrete
counterpart, which applies an operation to one set of n reals
yielding a “transformed” set of n reals. This problem has
applications in signal processing, interpolation methods, and
many other discrete problems.
The naive algorithm for computing the Fourier transform
of n reals requires approximately n 2 arithmetic operations
(adds and multiplies). The fast Fourier transform of Cooley
and Tukey 14 accomplishes this task in approximately n log 2 n
arithmetics. It achieves this by doing about n arithmetics on
each of log 2 n levels; in this sense it is quite similar to the
Mergesort algorithm discussed earlier. There are many dif¬
ferent expositions of the algorithm, such as those in Aho,
Hopcroft, and Ullman 15 or Borodin and Munro. 16 It is
interesting to note that in addition to being faster, many of
the numeric properties of the FFT are better than those of
the naive transform.
The fast Fourier transform has had a substantial impact on
computing. It forms the backbone of many “numeric”
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133
programs. Practitioners in diverse fields use the FFT to find
hidden periodicities of stationary time series. Signal proces¬
sing uses it in filters to remove noise from signals and eradicate
blurring in digital pictures. Numerical analysis utilizes it for
the interpolation and convolution of functions. Applications
of the FFT in such diverse areas as electrical engineering,
acoustics, geophysics, medicine, economics, and psychology
are listed by Brillinger. 17 Many special-purpose processors
have been built which implement this algorithm; some are
multiprocessors which operate in parallel. The FFT is also
widely used in the design of “discrete” algorithms. It is the
primary element in many algorithms which operate on poly¬
nomials, performing such operations as multiplication,
division, evaluation, and interpolation. Not surprisingly, it is
also employed in some of the fastest known algorithms for
operating on very long integers, such as multiplying two
1000-bit integers. We will see an application of this problem
later.
Matrix multiplication. One of the most common ways of
representing many different kinds of data is in a matrix, and
one of the most common operations on matrices is multipli¬
cation. How hard is it to multiply two n X m matrices? Using
the standard high school method takes about 2 n arithmetic
operations to calculate each of the n 2 elements of the product
matrix, so the total amount of time required by that algorithm
is proportional to « 3 . People have been multiplying matrices
by this method for a century. Surely this must be the best
possible way to multiply matrices-our intuition tells us that
we just can’t do any better.
The high school algorithm for multiplying two-by-two
matrices uses eight multiplications and four additions. It is
fairly counterintuitive to leam that the product can be com¬
puted using only seven multiplications at the cost of an
increase of 15 additions. But if that is counterintuitive, then it
is absolutely mindboggling to find that this fact alone allows
O-notation
Algorithm analysts frequently employ the "big-oh" notation
of mathematics. In this notation we can write an expression like
T(r>) =6n 2 + 9.3/? = 0(/? 2 )
to show the running time—T(/?)—of an algorithm. The more
accurate expression for T(/?) is much more complicated to ex¬
press than the simple 0(/? 2 ); we therefore see a tradeoff between
the accuracy of the statement and the ease of expressing the
formula (as well as the ease of deriving the expression). There is
a well-developed mathematical theory of "order arithmetic"
that allows derivations to be made without regard to the con¬
stant factors of the leading terms. Most calculations in this arith¬
metic are very simple.
"Big-oh" notation is a useful tool for analyzing algorithms.
The running times of most algorithms to within "big-ohs" are
much more easily obtained than are the exact analyses of the
algorithms. If we know that algorithm A takes 0(n 2 ) time and
that algorithm B takes 0(/7 log/?) time, then regardless of the
constants "hidden" in the notation, algorithm B will be faster
than algorithm A for large enough values of n. The "big-oh"
analysis will therefore be of great help in choosing an algorithm
that is to process a huge amount of data, as long as we are
careful not to be caught unaware by the constants hidden in the
notation.
us to construct an algorithm for multiplying n X n matrices
that runs in less than n 3 time! This algorithm, devised by
Strassen, 18 decomposes each n X n matrix into four (m/2) X
(m/2) matrices. It does seven multiplications of («/2) X
(m/2) matrices and then fifteen additions on matrices of that
size to fmd the product of the original matrices. Notice, how¬
ever, that the cost of those additions is proportional to n 2 . If
we let T(m) be the time required to multiply nX n matrices,
then T(n) satisfies the recurrence
T(l)=l,
T(m) = 7T(m/2) + 0(m 2 )
having the solution T(m) = 0(m 2-81 ) (where 2.81 is an approx¬
imation to log 2 7). The Strassen algorithm as originally
presented is less efficient than the high school algorithm until
n is in the thousands. Recent work, however, shows that it can
be practical when n is as small as 40. But practice aside, who
can help but be amazed by the fact that we can multiply
matrices faster than we thought we could?
The fast matrix multiplication algorithm provided the
basis for one of the all-time great revolutions in the history
of “theoretical” algorithm design, during which a number of
“best” known algorithms were toppled from their thrones.
Many of these were m 3 matrix algorithms which we can now
do in 0(n 2-81 ) time; among these are matrix inversion, LU
decomposition, solutions to systems of linear equations,
and calculations of determinants. A number of problems
which seemed to be totally unrelated to matrices were phrased
in terms of them. As a result 0(n 2 ' 81 ) algorithms followed
for such diverse problems as finding the transitive closure of
a graph, parsing context-free languages (an important problem
in compilers), and finding distances between n points in
Euclidean n -space. All of these algorithms stem from the fact
that two-by-two matrices can be multiplied with seven
multiplications.
Public-key cryptography. Communications systems which
deal with the problem of transmitting a message from a sender
to a receiver across an insecure and possibly bugged channel,
while protecting the privacy of the message, are known as
cryptosystems. Such security needs often arise in military
applications; they also promise to play an ever increasing
role in applications such as electronic mail and electronic
funds transfer. A cryptosystem is usually implemented by
encoding and decoding algorithms which transform their
inputs according to keys they are given. To send person X
message M we use the encoding algorithm and key to produce
message M', transmitting M' to X across the possibly insecure
channel. When X receives M' he uses the decoding algorithm
and key to determine M, while any “eavesdropper” has only
M'. One difficulty with this system is the distribution of keys
to the appropriate parties. This must usually be accomplished
by the use of expensive secure channels such as human
couriers.
An alternative, called a public-key cryptosystem, was
recently invented by Heilman and Diffie. 19 In their system
each person has an encoding key and a decoding key, as
before. To send a message to person X we encode it using X’s
encoding key, and then X can decode it with his decoding key.
The novel aspect of this system is that we can make the
encoding key public without revealing the corresponding
decoding key. We can then view the encoding key as the
address of X’s mail box, and anyone can put mail into that
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box simply by encoding the message. Actually unlocking the
box, however, requires the decoding key, which only X
possesses. Although such a system solves almost all of the
difficulties of previous cryptosystems, one major obstacle
remains; for most codes knowledge of the encryption key
immediately reveals the decryption key. Thus all we need to
complete our public-key cryptosystem is an appropriate
encoding/decoding algorithm, provided such an algorithm is
possible.
A suitable encoding/decoding method was recently
developed by Rivest, Shamir, and Adleman. 20 Their method is
based on algorithmic issues in the theory of numbers. They
view messages as multiprecision (long) integers of 200 decimal
digits, for example. The coding procedure then transforms
these messages by sophisticated use of modular arithmetic and
prime number theory. The transformations require many
sophisticated algorithms. For instance, the process of key
selection is based on fast algorithms for multiplying multi-
precision integers and testing such integers for primality; fast
mulliprecision exponentiation algorithms then perform
encoding and decoding. The fact that any method that
“breaks” the system must essentially find the factors of a very
large number is the basis of the system’s security. Although no
one knows precisely how difficult this factoring is, mathema¬
ticians have been working on the problem for many centuries,
and no one yet knows of a fast method. Let me put this in
perspective: if we deal with 200 decimal digit integers, then
the key selection, encoding, and decoding algorithms require
only a few seconds of CPU time; the best known method for
breaking the system, however, would require ten million
centuries of CPU time.
We have only scratched the surface of the fascinating field
of public-key cryptography. In addition to use in crypto¬
systems, these methods can also be used to provide “electronic
signatures,” i.e., verifications of identity. This cryptosystem is
another interesting example of the interactions between
theory and practice. It is based on number theory (perhaps the
purest of the areas of pure mathematics) and complexity
theory, yet it promises to revolutionize the practice or
cryptography. The interested reader should refer to the article
by Rivest, Shamir, and Adleman, cited above, or the
exposition in Gardner. 21 Although the algorithms we have
mentioned do not really solve an existing computational
problem, they solve a problem in a totally different area by
casting it in a computational light.
We have now examined five cases in which proper algorithm
design has led to a sophisticated algorithm that is much faster
than a naive algorithm. Algorithm designers have invested a lot
of work in developing these algorithms—but what difference
will it all make in practice?
To be honest, most of the time a fast algorithm makes no
difference at all. Rnuth has gathered empirical evidence
showing that most of the run time of a program is spent in
just three precent of the code. If an algorithm for a problem
is not in the critical three percent of a code, it makes little
difference if the algorithm is fast or not. A complicated algo¬
rithm is often a Lability rather than an asset. It will usually
mean more coding and more debugging time, and can some¬
times even increase the run time (when the overhead of
“starting up” a fancy algorithm costs more than the time it
saves).
Sometimes, however, a fast algorithm can make all the
difference in the world. If a certain computation is indeed the
bottleneck in the system flow, then an algorithm of half the
running time almost doubles system throughput. Many text
editors spend a vast majority of their time in string searching;
the fast algorithm for substring searching can speed up many
text editors by a factor of five. My experience with the search¬
ing program I mentioned in the introduction, where we
reduced the running time from three hours to five minutes,
is another good example of an appropriate use for a fast algo¬
rithm. In the inner loops of many programs proper algorithm
design is critical.
Fast algorithm design, although only occasionally yield¬
ing large financial savings, almost always gives us something of
a different value—a fundamental understanding of our compu¬
tation problems. This is usually reflected in cleaner programs;
but even more important is the understanding of how diffcult
it is to compute something. After a student has spent a month
or two investigating the problem of searching, he knows not
only how to search faster, but also why he can do it that fast
and why he can’t do it any faster. Such a student has learned
something of the foundations of his field.
Algorithm design—a systematic view
In the section above we saw a number of specific problems
and specific solutions; here we will show that there is more
to the field than isolated examples. Algorithm design is a co¬
herent discipline—one needs a specific set of concepts to
define a computation problem and specific set of tools to de¬
sign an optimal algorithm to solve it.
Problem dimensions—a microscopic view. The subset
testing problem showed that there can be many different
algorithms for solving a particular problem. In order to say
which one is best in a particular application we have to know
certain dimensions along which to measure properties of the
algorithm. For example, in one application we may need a
subset algorithm that must be very space-efficient and have
good worst-case running time; in another context, we might
have a lot of available space and only require good expected
running time, not caring if we infrequently must take a lot
of time. We have thus identified three dimensions of a compu¬
tational problem: time analysis, space analysis, and expected
vs. worst-case analysis. We will now investigate these and
other dimensions of computational problems.
Time and space analysis. The two most important re¬
sources in real computational systems are time (CPU cycles)
and space (memory words). These are therefore the two
dimensions of a problem most frequently studied. Running
time was the primary subject we examined in the examples
cited earlier. Most of the algorithms we discussed used very
little extra space after storing the inputs and outputs—the
hashing algorithm we used for subset testing was the only
exception. Since in large computer sytsems we can have huge
quantities of extra space for the asking and the paying, we
have often ignored the space requirements of algorithms.
With the rise in popularity of mini-and microprocessors with
very small memories, however, space analysis is once again
an important issue.
Model of computation. In covering the examples earlier
in this article, we were able to make reference to the time and
space requirements of various algorithms without reference to
their implementation on any particular computer. Our in¬
tuitive notions were robust enough to lead to sophisticated
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algorithms that would certainly beat their naive competitors
on any existing machine. But to analyze an algorithm in
detail we must have a precise mathematical model of the
machine on which the algorithm will run.
We could choose as our model a particular computer,
such as an IBM650 or a DEC-PDP-10, and then ask how many
microseconds of time or bits of storage a particular algorithm
requires. There are two problems with this approach. First,
we will problably analyze the expertise of the algorithm’s
implementer more than we will the algorithm’s intrinsic
merit; and second, once we have completed an analysis using
an IBM 650 we still know very little about the algorithm’s
behavior on a PDP-10. One way of dealing with these diffi¬
culties is to invent a representative computer and then com¬
pare the performances of competing algorithms on that
machine. Knuth 22 has described one such machine which he
named the MIX computer. It has much in common with most
existing machines without many idiosyncrasies of its own.
If algorithm A is faster than algorithm B when implemented
on MIX, then it is likely to be faster on most real machines,
too.
Another solution is not to analyze the implementation of
the algorithm on any particular machine at all, but simply to
count the number of times the algorithm performs some
critical operation. For the analysis of the FFT and matrix
multiplication we chose to count the number of arithmetic
operations. We know that the FFT uses exactly n log 2 n
multiplications. To estimate its running time for a given
implementation we can look up the execution speeds of the
instructions around the muliplication instruction, sum those,
and then multiply by n log 2 to get an estimate for the run¬
ning time. It is usually easy to determine the running time of a
particlar program if we know the number of times the critical
operation is to be performed. We must be careful, however,
not to ignore certain “bookkeeping” operations that may
become critical in implementations. Once we have chosen a
critical operation to count it is very easy to specify a model of
computation. To count arithmetic operations we usually
employ the “straight-line program” model in which an algo¬
rithm for a particular value of the problem size («) is repre¬
sented by a sequence of statements of the form
Xi*-X } OP x k
where OP is add, subtract, multiply, or divide. If the sequence
for a particular value of n is m instructions long then we say
that the execution time of our program is T(n) = m. If our
critical operation were comparison, then we would probably
choose the “decision tree” model. These and other models
are described by Aho, Hopcroft, and Ullman. 2 3
The above models allow us to analyze algorithms for their
suitability as “in-core” programs on single-processor mach¬
ines. If a program has very little main memory available and
must store most of its data on tape, then some tape-oriented
model such as the Turing machine is the most accurate model
of the computation. If a program is to be run on a multi¬
processor machine then our model must express this fact,
and the model employed will vary with the multiprocessor
architecture. The interested reader should refer to Kung 25
for a discussion of some of these issues from an algorithmic
viewpoint. Many other models of computation have been
proposed to describe diverse computing devices. The two
important things in choosing a model are that it be realistic ,
so the results will apply to the situation it purports to model,
and that it be mathematically tractable, so we can derive
those results.
Exact or approximate analysis. Once we have chosen a
model of computation we can analyze an algorithm’s perform¬
ance by counting the resources (time or space) it uses as a
function of n, the problem size. How accurately sho.ild we
do that counting? We could be very precise, calculating the
answer exactly, or we might settle for an approximate answer.
There are levels of approximation, all the way from the first
two terms of the answer to rough upper and lower bounds.
It is certainly desirable to get the exact answer, but this is
sometimes very difficult. The first one or two terms of the
cost function are adequate for most purposes, and in many
cases we need only the function’s asymptotic growth rate.
We saw in the subset testing problem an example in which the
run time for one program was 138 hours while another pro¬
gram ook just 4 seconds to carry out the same task. Ewn if
our analysis had missed a factor of ten, that could not affect
our choice for large problems.
We often use the “big-oh” notation to describe the com¬
plexity of a problem. No matter what the respective constants
are, an o(n log 2 n) algorithm will be faster than an 0(n 2 )
algorithm for large enough n. As we solve larger and larger
problems by computer, we are more and more frequently in
the domain of “large enough n.” Asymptotically fast algo¬
rithms also have another advantage. If we get a new machine
one hundred times faster than our old one, using an 0(n log 2
n) algorithm will allow us to solve a problem almost one
hundred times larger in the same period of time. Using an
0(« 2 ) algorithm will permit the new machine to solve a prob¬
lem only ten times larger in that time. Thus, a function’s
asymptotic growth rate is usually enough to tell us how
much an increase in problem size will cost under each type
of algorithm.
Average or worst-case analysis. Many algorithms perform a
sequence of operations independent of their input data; the
FFT and matrix multiplication algorithms are both data-
independent. The analysis of a data-independent algorithm is
straightforward—we simply count the number of operations
used. The operation of algorithms such as those for sorting and
substring searching, however, are dependent on their input
data. One algorithm can have very different running times for
two inputs of the same size. How do we describe the running
time of such an algorithm? Pessimists want to know the worst-
case running time over all inputs and realists want to know the
average running time. (We are rarely concerned with the best-
case running time, for there are very few optimists in
computing.)
Most mathematical analysis of algorithms has been done for
the worst case. Even in data-dependent algorithms it is usually
easy to identify the worst possible occurrence and analyze it as
in a data-independent algorithm. In certain applications (air
traffic control is often cited) it is important to have an algo¬
rithm that never surprises us with a very slow case. For most
applications, however, we are more interested in what will
usually happen; expected-time analysis provides this informa¬
tion. Relatively little work has been done on expected-time
analysis. The two major stumbling blocks are in the choice of
a realistic and tractable probability model of the inputs and in
the intrinsic difficulty of dealing with expectations instead of
single cases. It would be desirable to have a single algorithm
efficient in both expected and worst-case performances.
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Upper and lower bounds. Most naive sorting algorithms
(such as “bubble sort”) require 0 (n 2 ) comparisons in the
worst case. Earlier we investigated Mergesort, which never uses
more than 0(nlog 2 n) comparisons. Should we continue our
search, hoping to find an algorithm that uses perhaps only
0 (n) comparisons? The answer to this question is no, for we
can show that every sorting algorithm must take at least
C)(nlog 2 n) comparisons in the worst case. The proof of this
Decision trees
This figure illustrates a decision tree program to sort three
numbers. The program "starts" at the top node and compares
the value of a with the value of b. If a is the lesser it goes down
the left branch of the tree and if a is greater it goes down the
right branch (we assume for clarity that all elements are dis¬
tinct). It continues until it reaches a "leaf" (leaf nodes are de¬
picted by rectangles); when we arrive at a "leaf" we know the
total ordering of a, b. and c. I encourage the reader to study this
example to see that it correctly sorts the three elements.
Decision trees accurately model computations based on com¬
parisons. Theoretically, we can represent any comparison-based
program for sorting n numbers with a corresponding decision
tree. For example, we can "translate" the above tree into a set
of nested IF statements in a high-level programming language.
We can use the mathematical properties of decision trees to
prove lower bounds on the complexity of certain computations.
Notice that the height of the decision tree (i.e., the maximum
distance from the root to one of the leaves) corresponds to the
maximum number of comparisons ever used by the "decision
tree program." It is a well-known mathematical fact that if a
binary tree hasm leaves, it must have neight of at least log 2 m. It
is also known that there are n! (i.e., n*(r»-1)*...*1) dif¬
ferent permutations of n elements. Since a sorting program
must correctly distinguish between all permutations of its
input variables, its decision tree must have at least n\ leaves.
Combining these two facts, we see that any decision tree for
sorting must use at least log 2 n! comparisons, which is ap¬
proximately n log 2 n. We thus see that the Mergesort algorithm
for sorting is very close to the best possible algorithm in terms of
number of comparisons used.
We must be very careful in interpreting lower bounds—they
only apply in the given model of computation. It might be
possible to sort numbers faster if we use more powerful opera¬
tions than comparisons. (In fact, it is!) The lower bound, how¬
ever, still serves a useful purpose. It tells us that if we want to do
something faster, we had better adopt a fundamentally different
approach to solving the problem.
theorem uses the “decision tree” model of computation,
described nicely by Aho, Hopcroft, and Ullman. 24 The
Mergesort algorithm gave us an upper bound of 0(«log 2 n) on
the complexity of sorting; this theorem gives us a lower
bound. Since the two have the same growth rate, we can say
that Mergesort is optimal to within a constant factor under the
decision tree model of computation. Notice that we have now
made the important jump from speaking of the complexity of
an algorithm to speaking of the complexity of the problem.
Lower bound results are usually much more difficult to
obtain than upper bounds. To find an upper bound we need
only give a particular algorithm and analyze it. For a lower
bound, however, we must show that in the set of algorithms
for solving the problem there are none more efficient than the
lower bound. There are some trivial lower bounds we can
easily achieve: most problems require examination of all their
inputs, so we usually have an easy lower bound of the input
size. The number of nontrivial lower bounds discovered to
date is very small.
A precise model of computation is important in proving
lower bounds. Previously we gave three algorithms we can use
for testing set equality: brute force, sorting, and hashing. We
gave them originally for subset testing, but recall that two sets
are equal if and only if each is a subset of the other. The
importance of the computational model becomes clear when
we leam that we can prove each of those algorithms optimal
under different computational models! Brute force’s 0(n 2 )
performance is optimal if only equal/not-equal comparisons
can be made between elements of the two sets. If the model of
computation includes only less-than/not-less-than compari¬
sons, sorting’s 0(nlog 2 n) comparisons are optimal. If the
model is a random access computer such as MIX, hashing’s
average-case linear performance is provably best.
Exact and approximation algorithms. The best-known
algorithms for many problems are quite slow, requiring, say,
0(2”) time. A very few of these problems have actually been
proved to have exponential lower bounds. Others belong to a
fascinating class called the NP-complete problems, either all
solvable in time polynomial in problem size, or all of expo¬
nential complexity. Unfortunately, nobody yet knows which,
but most of the money is on exponential. Examples of NP-
complete problems include the traveling salesman problem
(finding a minimal-length tour through a set of cities), bin
packing, and the knapsack problem. Literally hundreds of
problems are known to be NP-complete. Lewis and
Papidimitriou 26 provide an excellent introduction to this class.
There are other problems, not proven to be hard, for which no
one has yet been able to design fast algorithms. So when we
have a problem we don’t know how to solve efficiently, what
can we do?
The answer is amazingly simple: don’t solve it. Solve a
related problem instead. Instead of designing an algorithm
to produce the exact answer, we can build one to produce an
approximation to the exact answer. So instead of finding a
minimal tour for the traveling salesman, we might provide
him with a tour we know is no more than 50 percent longer
than the true minimum. Or if someone asks if a number is
prime or composite, instead of providing the true answer
we might respond “I don’t know, but I’m 99.999999 percent
sure that it’s prime.” Problems abound for which the best
known exact algorithms require exponential time, but for
which we can quickly find approximate solutions. Garey and
Johnson 27 examine these issues.
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These problem dimensions—such as time analysis, space
analysis, and expected vs. worst-case analysis—are the
categories in which algorithm designers think. When someone
brings a designer a problem, his first task is to understand the
abstract problem. Next he must understand what kind of solu¬
tion the person wants, and he uses the dimensions to describe
the desired solution. Using the vocabulary introduced here it
is easy to describe concepts such as a “fast expected time and
low worst-case storage approximation algorithm for task X, to
be run on a multiprocessor machine.” There are other infre¬
quently used dimensions we have not covered, such as code
complexity—how long is the shortest program to solve a
problem? But the dimensions we have examined can describe
most algorithmic results.
Problem areas—a macroscopic view. The vocabulary above
can describe a particular algorithmic problem at a precise level
of detail. Here we change our perspective and examine large
classes of problems, but use the same terminology.
Ordered sets. There are many problems on sets that depend
only on a “less than” relationship being defined between the
elements of the set. In many cases the set contains integers or
real numbers, while in other cases we define a “less than”
relation between character strings (JONES is less than
SMITH). The problems discussed earlier in the section on
subset testing all deal with ordered sets. The algorithms in that
section are appropriate if the elements of the sets are numbers,
character strings, or any other type of “orderable” object.
Knuth 28 provides an excellent introduction to the applications
of, and algorithms for, ordered sets.
The “median problem” is another problem defined for
ordered sets: given an n -element set we are to find an element
which is less than half of the elements and not less than the
other half. A naive algorithm would count for each element
the number of elements less than it, and then report the medi¬
an as the element with exactly half the others less than it. This
algorithm makes approximately n 2 comparisons. We can devise
an 0(nlog 2 n) algorithm by sorting the elements and then
reporting the middle of the sorted list. In 1962 C. A. R. Hoare
described an algorithm for the median problem, with linear
expected time. For over ten years no one knew if there was an
algorithm with linear worst-case time; Blum et al. finally
offered one in 1973. 29 Much additional work has been done
on this problem, exploring facets such as minimal storage,
detailed worst-case vs. expected running time analysis (upper
and lower bounds), and approximation algorithms.
Algebraic and numeric problems. Many aspects of algebraic
and numeric problems have a discrete flavor, and discrete algo¬
rithm design can play a significant role in such problems.
Matrix multiplication is perhaps the clearest example: we can
describe (and appreciate) the fast algorithm without reference
to any of its numeric properties. We can also view the FFT
“non-numerically.” Another numeric problem that can
assume a purely discrete character is sparse matrix manipula¬
tion (in a sparse matrix almost all elements are zero). Borodin
and Munro, cited earlier, describe applications of discrete
algorithm design to numeric problems such as polynomial
manipulation, extended precision arithmetic, and multi¬
processor implementations of numeric problems.
Graphs. Graphs can represent many different kinds of
relations, from the interconnections of an airline system to the
configuration of a computer system. Taijan’s survey 30 dis¬
cusses many computational problems relating to graphs. One
important problem involves determining if we can imbed a
given graph in a plane without any edges crossing. We might
use this to check if we can imbed the connections of a given
circuit on a printed circuit board or integrated circuit. The
first algorithms for testing planarity ran in 0(« 3 ) time on
n-node graphs; after much effort by many researchers,
Hopcroft and Taijan finally designed a linear-time planarity
algorithm in 1974. 31 Another graph problem is constructing a
minimal spanning tree of a weighted graph, i.e., a minimal-
weight set of edges connecting all nodes. Researchers have
proposed and analyzed a wide variety of algorithms for tliis
problem. Some are superior for very dense graphs, others for
relatively sparse graphs, and still others for planar graphs. Effi¬
cient graph algorithms exist for problems such as computer
program flow analysis and finding maximal flows in networks.
And since a sparse matrix is usually represented by a graph,
graph algorithms can apply to sparse matrix problems.
Geometry. Shamos’ paper 32 is an outstanding introduction
to computational geometry, the field concerned with
developing optimal algorithms for geometric problems. Many
application areas are inherently geometric (such as circuit
layout) and other problems can be viewed geometrically (such
as treating a set of multivariate observations as points in a
multidimensional space). Shamos describes an important
structure, the Voronoi diagram, which allows many geometric
problems dealing with n points in a plane to be solved in
0(«log 2 n) time. Among these are determining the nearest
neighbor of every point, and constructing the minimal span¬
ning tree of the point sets, both important tasks in many data
analysis procedures and previously requiring 0 (n 2 ) time.
Many other important problems have been solved after being
cast in a geometric framework. One result, for example,
revealed that the standard simplex method of linear pro¬
gramming is not optimal for two - and three-variable programs
with n constraints. The simplex method has worst-case
running times of 0(n 2 ) and 0(n 3 ), respectively; an
0(nlog 2 n) method has proved optimal for both the two- and
three-variable case.
Other areas. We have glimpsed a few fields studied lay
algorithm designers. The results in many other areas must go
unmentioned. These include algorithms for problems in
compilation, operations research, data base management,
statistics, and character string handling. These results have led
both to fast algorithms and to a new algorithmic under¬
standing of the various fields.
The “building blocks” of algorithm design. Wandering
through a computer room we cannot help but be impressed by
the complexity of a large-scale computing system. The novice
might find it hard to believe that the human mind could design
anything so complicated. Although he is not too far from the
truth, many undergraduates are able to understand the basics
of computer organization after only one or two semesters.
They are able to comprehend the complexity not by sheer
force of concentration, but rather by understanding the
“building blocks” from which computers are made. A similar
experience awaits the novice algorithm designer. The algo¬
rithms surveyed above deal with many problem areas, but are
rather simple to comprehend once we understand the
“building blocks” of algorithm design. Here we will describe
three important classes of these “blocks.”
Data structures. Algorithms deal with data, and the algo¬
rithm designer uses data structures as tools to organize data.
Earlier we saw simple data structures such as arrays and
matrices, and a fairly complex data structure, the hash table.
Number 44
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
There are more exotic types, such as linked lists, stacks,
queues, priority queues, and trees. Each provides an appro¬
priate way to structure data for a particular task. Taijan 33
briefly describes many of these structures; Knuth 34 provides
detailed descriptions of a large number of interesting
structures.
Algorithmic techniques. Structured programming demands
that a programmer express a complicated sequence of
commands as a series of refinements by which the program can
be understood at different levels. In each of these refinements
the programmer applies a basic, well understood method to a
well defined problem. Good programmers used this technique
long before it was verbalized; good algorithm designers use a
similar strategy even though they infrequently discuss it. The
constructs available to the algorithm designer are similar to
those available in structured programming, though somewhat
more powerful. We will describe some of these constructs very
briefly; more detail can be found in Taijan 35 and Aho,
Hopcroft, and Ullman. 36
We have already seen many common algorithmic con¬
structs. Most of the algorithms we described use iteration in
one form or another—this says “do x over and over until the
task is accomplished.” Iteration is present in almost all pro¬
gramming languages as DO and WHILE loops. A more power¬
ful construct is recursion, giving us a way to express recursive
problem solving in programming languages. To define a
recursive solution to a problem we say (essentially) “to solve a
problem of a certain size, solve the same problem of a smaller
size.” We used recursion to describe a binary search: to binary
search a table of size n we binary searched a table of size n /2.
A particular application of recursion, divide-and-conquer, says
“to solve a problem of size n, first divide it into subproblems
each of size only a fraction of n, then solve those subproblems
recursively, and finally combine the subsolutions to yield a
solution to the original problem.” We can view Mergesort as
a textbook example of divide-and-conquer: to sort a list of
n elements we first break the list into two sublists each of
n/2 elements, then sort those recursively, and finally merge
those together. The FFT and the 0(n 2M ) matrix multiplica¬
tion algorithms are other applications of the divide-and-
conquer technique. Once we understand the fundamental
principles of divide-and-conquer algorithms, we can easily
grasp each of these instances.
Researchers have identified and studied many other algo¬
rithmic techniques. Dynamic programming, a technique from
operations research, has found many applications in algorithm
design. Search strategies such as breadth-first search and
depth-first search have yielded efficient graph algorithms.
Transformation allows us to turn an instance of one problem
into another; we saw earlier that there are many transforma¬
tions to turn almost totally unrelated problems into instances
of matrix multiplication. Perhaps the single most important
algorithmic tecnhique is the use of optimal tools to solve the
subproblems we create for ourselves in designing a new algo¬
rithm.
Proof techniques. Once an algorithm designer has devised
an algorithm and “knows in his heart” that it has certain
properties, he must prove that it does. (Perhaps this separates
practitioner from theorist.) He must first prove that his algo¬
rithm indeed computes what it purports to; he will use many
of the tools of program verification here. Next he must
analyze his algorithm’s resource requirements, using many
different mathematical tools. Finally he must prove his algo¬
rithm optimal by giving a lower bound proof. Weide 37 dis¬
cusses the different methods of analysis used in these steps.
Current directions
Algorithm design has grown rapidly in the past decade.
Essentially unknown as a field ten years ago, it is not one of
theoretical computer science’s most active areas and sees wide¬
spread use in applications. Continued emphasis on
performance ensures even more algorithm research. Here we
will examine some of the directions in which the field is
moving.
One constant trend has been from “toy” problems to
“real” problems. This involves many detailed analyses and
expected-resource analyses, for in applications we are often
seriously concerned about 20-percent differences in average
running time. Much recent work has centered on approxima¬
tion algorithms, since many applications do not require exact
answers. On the theoretical side, the outstanding question is
the complexity of the NP-complete problems—are they
exponential or not? Another important theoretical problem is
the search for some underlying theory of algorithm design; we
still have no theoretical explanation for what makes a class of
problems easy or hard. Taijan has mentioned the need for a
“calculus of data structures”—a set of rules leading to the best
possible structure for a given situation.
An outgrowth of this work will be the development of
“algorithm engineering.” This field will supply the program¬
mer with tools similar to those electrical engineering gives the
circuit designer. Before algorithm design turns into algorithm
engineering we will need to develop many more specific algo¬
rithms and provide a theoretical base for the field. We will
know that the field has become an engineering discipline as
soon as theoretical computer scientists assert that designing
algorithms is no longer bona fide research because “it’s such a
well-understood process.”
Algorithm design offers much to individuals involved in
computing-related activities. The mathematician and theo¬
retical computer scientist can view the field as a rich source
of problems needing precise mathematical treatment. These
problems are mathematically fascinating and call for some of
the most powerful tools of discrete mathematics. The applica¬
tions programmer with little interest in elegant theorems can
also benefit, since proper algorithm design occasionally yields
significant financial savings. But even placing aside benefits to
specific practitioners, I feel that anyone involved with com¬
puting, regardless of his position in the practical-to-theoretical
continuum, should have some familiarity with the field. The
study of algorithms is the study of the very heart of
computing, and it provides us with a new way of thinking
about our computational problems.
Acknowledgments
This paper has profited from the helpful criticism of many
people; the comments of David Jefferson, Len Shustek, and
Bruce Weide have been particularly helpful. The research
described here was supported in part by the Office of Naval
Research, under Contract N000014-76-C-0370.
Page 14
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Number 44
139
References
1. J. E. Hopcroft, “Complexity of Computer Computations,”
Proc. IF1P Congress 74, Vol. 3, 1974, pp. 620-626.
2. R. E. Taijan, “Complexity of Combinatorial Algorithms,” SIAM
Review, Vol. 20, No. 3, July 1978, pp. 457-491.
3. B. Weide, “A Survey of Analysis Techniques for Discrete Algo¬
rithms,” Computing Surveys, Vol. 9, No. 4, Dec. 1977, pp.
291-313.
4. D. E. Knuth, “Mathematical Analysis of Algorithms,” IFIP
Congress 71, Vol. 1, 1971, pp. 135-143.
5. D. E. Knuth, “Algorithms,” Scientific American, Vol. 236, No.
4, Apr. 1977, pp. 63-80.
6. A. V. Aho, J. E. Hopcroft, and J. D. Ullman, The Design and
Analysis of Computer Algorithms, Addison-Wesley, Reading,
Mass., 1974.
7. D. E. Knuth, The Art of Computer Programming, Volume 1:
Fundamental Algorithms, Addison-Wesley, Reading, Mass.,
1968. *
8. D. E. Knuth, The Art of Computer Programming, Volume 2:
Seminumerical Algorithms, Addison-Wesley, Reading, Mass.,
1969.
9. D. E. Knuth, The Art of Computer Programming, Volume 3:
Sorting and Searching, Addison-Wesley, Reading, Mass., 1973.
10. Knuth, Art of Computer Programming, Volume 3, p. 391.
11. Knuth, Scientific American, Vol. 236, No. 4, Apr. 1977, p. 63ff.
12. D. E. Knuth, J. H. Morris, and V. R. Pratt, “Fast Pattern Match¬
ing in Strings,” SIAM Journal of Computing, Vol. 6, No. 2, June
1977, pp. 323-350.
13. R. S. Boyer and J. S. Moore, “A Fast String Searching Algo¬
rithm.” CACM, Vol. 20, No. 10, Oct. 1977, pp. 762-772.
14. J. M. Cooley and J. W. Tukey, “An Algorithm for the Machine
Calculation of Complex Fourier Series,” Mathematics of
Computation, Vol. 19, 1965, pp. 297-301.
15. Aho, Hopcroft, and Ullman, Design and Analysis..., pp. 252-
276.
16. A. Borodin and I. Munro, The Computational Complexity of
Algebraic and Numeric Problems, Elsevier-North Holland Pub.
Co., N.Y., Theory of Computation Series No. 1, 1975.
17. D. R. Brillinger, Time Series: Data Analysis and Theory, Holt,
Rinehart, and Winston, N.Y., 1975.
18. V. Strassen, “Gaussian Elimination is Not Optional,” Numerishe
Mathematik, Vol. 13, 1969, pp. 345-356.
19. W. Diffle and M. Heilman, “New Directions in Cryptography,”
IEEE Trans. Information Theory, Vol. IT-22, No. 6, Nov. 1976,
pp. 644-654.
20. R. L. Rivest, A. Shamir, and L. Adleman, “A Mathod for Obtain¬
ing Digital Signatures and Public-Key Cryptosystems,” CACM,
Vol. 21, No. 3, Feb. 1978, pp. 120-126.
21. M. Gardner, “A New Kind of Cipher That Would Take Millions
of Years to Break” (Mathematical Games), Scientific American,
Vol. 236, No. 8, Aug. 1977, pp. 120-125.
22. Knuth, Art of Computer Programming, Volume 1, pp. 120-160.
23. Aho, Hopcroft, and Ullman, Design and Analysis..., pp. 2-41.
24. Ibid., pp. 24-25.
25. H. T. Kung, “Synchronized and Asynchronous Parallel Algo¬
rithms for Multiprocessors,” in Algorithms and Complexity:
New Directions and Recent Results, J. F. Traub, Ed., Academic
Press, N.Y., 1976, pp. 153-200.
26. H. R. Lewis and C. H. Papidimitriou, “The Efficiency of Algo¬
rithms,” Scientific American, Vol. 238, No. 1, Jan. 1978, pp.
97-109.
27. M. R. Garey and D. S. Johnson, “Approximation Algorithms for
Combinatorial Problems: An Annotated Bibliography,” in
Algorithms and Complexity: New Directions and Recent Re¬
sults, J. F. Traub, ed.. Academic Press, N.Y., 1976, pp. 41-52.
28. Knuth, Art of Computer Programming, Volume 3.
29. M. Blum, R. Floyd, V. Pratt, R. Rivest, and R. Taijan, ‘Time
Bounds for Selection,” Journal of Computer and Systems
Sciences, Vol. 7, No. 4, Aug. 1973, pp. 448-461.
30. Tarjan, SIAM Review, Vol. 20, No. 3.
31. J. Hopcroft and R. Taijan, “Efficient Planarity Testing,” JA CM,
Vol. 21, No. 4, Oct. 1974, pp. 549-568.
32. M. I. Shamos, “Geometric Complexity,” Proc. Seventh ACM
Symposium on the Theory of Computing, 1975, pp. 224-233.
33. Taijan, SIAM Review, Vol. 20, No. 3.
34. Knuth, Art of Computer Programming, Volume 1.
35. Taijan, SIAM Review, Vol. 20, No. 3.
36. Aho, Hopcroft, and Ullman, Design and Analysis..., pp. 44-74.
37. Weide, Computing Surveys, Vol. 9, No. 4, pp. 291-313.
Jon Louis Bentley is an assistant professor of computer science and
mathematics at Carnegie-Mellon University, Pittsburgh, Pennsylvania.
He worked as a research intern at the Xerox Palo Alto Research Center
from 1973 to 1974. During the summer of 1975 he was a visiting
scholar at the Stanford Linear Accelerator Center. From 1975 to 1976
he was a National Science Foundation graduate fellow. His current
research interests include the design and analysis of computer algo¬
rithms (especially for geometrical and statistical problems) and the
mathematical foundations of computation.
A member of the ACM and Sigma Xi, Bentley received the BS in
mathematical sciences from Stanford University in 1974, and the MS
and PhD in computer science from the University of North Carolina
in 1976.
Number 44
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Dr. Dobb's Journal of Computer Calisthenics 8i Orthodontia, Box E, Menlo Park, CA 94025
Page 15
ALL THE SECRETS
YOU EVER WANTED
.ABOUT POLY 88 BASIC
BY MARVIN A. KONOPIK
American Embassy
AF'O San Francisco 96503
I have broken some of the
secrets of the Poly 88 BASIC
version A00 that might be help¬
ful to others in understanding
their BASIC as well, or at least
help to get a handle on it. The
Poly BASIC Manual contains a
great deal of technical informa¬
tion, but the many ways this
information can be used is not
fully explained. After retyping a
program for the third time,
I threw in the towel, and decided
there must be an easier way.
So, I have listed below some
short-cuts that make computer
life a whole new game and a lot
more fun.
SCR is a dirty word: type
SCR or LOAD and all is lost!
Wrong . . . The key to the prob¬
lem is in location 205D and 205E.
The address listed here tells you
where BASIC started loading
your program. Go to that loca¬
tion, and scroll ahead. You will
see several rows of zeros, which
is what SCR is all about. Scroll
ahead further and look through
the memory until you see an 0D.
This is the Carriage Return in
Hex. Remember the memory
| location of the 0D. Put this
1 location into position 205D, type
j in the warm start SPJ2003
and a G and your program is
up. Restore your program, record
it onto tape, and after you
verify it, reload your BASIC
and continue. I have never re¬
loaded my BASIC; it seems to
operate perfectly with the new
| starting point, but why take a
1 chance. You lost the first couple
of lines, but this is no big deal.
Next time begin your programs
with a full REM line of 63 spaces,
j to minimize your losses in case
| of an accident.
If that was easy, then try
the following hard way for greater
l program salvage. Using the solu¬
tion above, you have lost some
valuable program material be¬
tween the end of the zeros and
the first 0D. This may have been
valuable text that SCR or LOAD
j did not destroy, but which you
did. If you want to restore your
program and minimize the losses,
| call up location 205D to see
where your program starts. Go to
the location shown in 205D and
you should see 0D and several
lines of zeros. Hit the spacebar
to go to the next location after
the 0D. There is probably an 01
already in that box, but load 2C
into it. 2C is Hex for 44. Now
back up until the 0D is in the
memory window again. Now hit
the spacebar 44 times and if the
memory is still full of zeros,
type in an 0D. Use control H
or LF back to the location follow¬
ing the 2C. You can use any
number instead of 2C, except that
44 should be near the last of the
zeros and it seems to work about
right. Put in a 01 00 8F and
fill the remaining locations with
20 until you reach the 0D that
you just loaded. As you may have
guessed, the first 2C was the
length of the line from 0D to 0D.
The 01 00 was the wasy BASIC
stores line number 0001, the 8F is
what BASIC calls REM when it
stores it into memory, and the
20s are all spaces in Hex. You
have just typed in a REM line
of 40 or so spaces in BASIC,
the hard way. Now for line 0002.
In the next block after the OD of
line 0001 that you just typed, put
in FF so you can find it easily
later. Back up again to the 0D be¬
fore the FF and count the number
of spacebar hits until the next
0D appears. Write this number
down. If this number is less than
64, then continue, if not, read
on, I’ll help you later. Your
number, which is less than 64,
should be converted to HEX
and put in place of the FF you
previously loaded as the start
of line 0002. The next locations
will be 02 00 8F and the re¬
maining zeros should be filled
with 20’s as you did in line one.
If you had over 64 in your
count, then re-do the procedure
above for line 0001 using 40
(64 decimal) or some number in
between, to lengthen line 0001
until the OD is closer to the end
of the zeros and the beginning of
the program to be saved. Another
way is to make a very short line
0002 and use 0003 for the first
partial line to be salvaged. The
drawback is that 3 could be too
high if only line 01 was lost, and
you had line 2 twice. Another way
out is to renumber the next line
since you now know how they
are stored in memory by the
BASIC program. Now that you
have filled all the zeros with
something, type in your warm
start location, and your program
should be there with the fust
partial line of your program
included on the end of a REM
line, but at least it is not lost.
If it did not come up, you simply
miscounted your line length, so
go back and count again. If it
still will not come up, look ahead
in memory and practice counting
the lines there between OD’s
until you have the system down
pat and then try again.
Merging programs is a com¬
plicated procedure! Not Really.
Before you load BASIC, Hit
Cmnd Z, and load the following
machine program into memory
starting at location 2000. 97 21
09 20 77 23 C3 04 20 and then
SPJ2000 and a G. When the
screen flashes bright white, all
memory has been set to zeros.
Now load in BASIC and your first
program. Type REN 1,1 and
LIST your program. Remember
to copy the last line number on
a piece of paper so you don’t
forget it. Hit Cmnd Z and scroll
through the memory a hundred
lines or so at a time, starting at
4A00 until you find the zeros.
Back up until you find the last
0D of the program, before the
zeros start. Write down this
memory location, and call up
location 205D. Also remember
the numbers that are in 205D:
you will need them later. Load
the location of the last 0D into
205D and 205E. Type in SPJ2000
(cold start) and a G. Load the
next program just like you did
the first. Type LIST to see if
the second program is there.
RENumber it, but use a number
higher than the last line of the
previous program. Do a Cmnd Z
again, and change location 205D
back to what it originally was,
and Warm Start your program
using 2003. Hit LIST, and be¬
hold! Two programs in a row.
Mark down the new last line
number, go back to the memory
to check for the last 0D again,
change location 205 D to this
location, cold start 2000, load
the third program, return 205D
to its original state, warm start
on 2003 and you’re up with
3 programs in a row.
You bought a printer and now
you found out that you cannot
warm start and save either the
program or the printer/driver!
It’s simple: change the data at
location 4A4D from 00 20 to
03 20 and warm start using 49C0.
You can re-record BASIC this
way, but dump from locations
2000 through at least 4C02
just to be safe. BASIC will now
always come on warm, but you
may occasionally have to do a
SCR before you can load your
programs. If you zeroize memory
before you re-record BASIC,
it will not load. You may have to
load a small program to put some
text in the buffer first, but it’s
worth the effort to have 2003
in location 4A4D when you need
it for a warm start and still retain
the use of the Printer/Driver.
Can’t warm start your Assem¬
bler? I cannot find this in the
manual. I guess the Poly people
thought everybody should go
around retyping lost programs
even if it took days. Well I did
my share of retyping and then
discovered that when you type
MNTR you can return to the
Editor by hitting a G. For this,
Poly puts the address 20FF in
the program counter. So if Poly
can do that, you can too, and
warm start any time you have a
lock up by using 20FF.
Have you ever wanted to
exchange text in the Editor, or
switch the end of your Assembler
program to the beginning and the
beginning to the end? Rather than
retype it, let the Editor help you.
Dump the text on tape and make
a note of the length of the dump
as well as the reading of the index
counter on the recorder. For
instance, we want the last half
first and the first half last. KILL
the old text from memory,
and back the recorder up half
way. Now load from that point
onward to the end. When you hit
the end, rewind to the beginning
and start loading again until you
feel you have loaded all the text
on tape somewhere at least one
time. Delete duplicate text and
tidy it up for use. I am not a
very fast typist, but watch me go
with the delete and Cmnd X line
remover. Using this procedure,
you can load bits and pieces of
different programs together into
one blend.
So much for the serious part
of life! Do you want some fun?
Type ‘flip’ in small letters while
you are up in BASIC. It reverses
the keyboard. You, who have to
use this, probably don’t think
it’s funny, but it makes.the key¬
board the damdest thing you
have ever tried to type with.
The data stored at location
205D shows where BASIC begins
storing your program in memory.
I hope somebody can find the
location where BASIC stores the
last 0D (CR) of the program, if
there is a location.
And so as you see, the discov¬
eries go on, and on, and on,
and each time, life becomes a
little easier with Poly.
Page 16
Dr. Dobb's Journal of Computer Calisthenics 8< Orthodontia, Box E, Menlo Park, CA 94025
Number 44
141
A SYNTAX-ORIENTED
COMPILER WRITING LANGUAGE
BY D. V. SCHORRE
UCLA Computing Facility
University of California at Los Angeles
Los Angeles, California
© 1964, Association for Computing Machinery, Inc.
Reprinted by Permission
Introduction
This classic paper describes a metacompiler developed as a project
of the Los Angeles Chapter of SIGPLAN, the Association for Com¬
puting Machinery’s special interest group in programming languages.
Several artifacts of the time appear-the use of ”rather than
and the use of “/" rather than “ I ” is due to the limited character set
on the IBM 026 keypunch. The original Meta II ran on the IBM 1401,
a machine with limited resources by today’sstandards. We’ve reprinted
it here because it is still a good tool for experimenting with languages
and their implementation. To install a Meta II system on your com¬
puter, you must hand-compile the Meta II compiler given in the article
(an instructive exercise in itself] and write an interpreter for the Meta II
machine in some suitable language (Microsoft BASIC wouldn't be a bad
choice). To check the whole thing, the compiler should compile itself
exactly. If not, fix the bug(s) and try again. In the end, you ’ll have a
nice tool for experimenting with programming languages and learn a
bit about the compiling process to boot. - Dennis R. Allison
META II is a compiler writing language which consists of syntax
equations resembling Backus normal form and into which instructions
to output assembly language commands are inserted. Compilers have
been written in this language for VALGOL I and VALGOL II. The
former is a simple algebraic language designed for the purpose of
illustrating META II. The latter contains a fairly large subset of
ALGOL 60.
The method of writing compilers which is given in detail in the
paper may be explained briefly as follows. Each syntax equation is
translated into a recursive subroutine which tests the input string for a
particular phrase structure, and deletes it if found. Backup is avoided
by the extensive use of factoring in the syntax equations. For each
source language, an interpreter is written and programs are compiled
into that interpretive language.
META II is not intended as a standard language which everyone
will use to write compilers. Rather, it is an example of a simple working
language which can give one a good start in designing a compiler-
writing compiler suited to his own needs. Indeed the META II compiler
is written in its own language, thus lending itself to modification.
Reprinted from the Proceedings of the 19th National Conference of
the Association for Computing Machinery, 1964.
History
The basic ideas behind META II were described in a series of three
papers by Schmidt, 1 Metcalf, 2 and Schorre. 3 These papers were
presented at the 1963 National A.C.M. Convention in Denver, and
represented the activity of the Working Group on Syntax-Directed
Compilers of the Los Angeles SIGPLAN. The methods used by that
group are similar to those of Glennie and Conway, but differ in one
inportant respect. Both of these researchers expressed syntax in the
form of diagrams, which they subsequently coded for use on a com¬
puter. In the case of META II, the syntax is input to the computer in a
notation resembling Backus normal form. The method of syntax
analysis discussed in this paper is entirely different from the one used
by Irons 6 and Bastian. 7 All of these methods can be traced back to the
mathematical study of natural languages, as described by Chomsky. 8
Syntax Notation
The notation used here is similar to the meta language of the
ALGOL 60 report. Probably the main difference is that this notation
can be keypunched. Symbols in the target language are represented as
strings of characters, surrounded by quotes. Metalinguistic variables
have the same form as identifiers in ALGOL, viz., a letter followed by
a sequence of letters or digits. Items are written consecutively to
indicate concatenation and separated by a slash to indicate alternation.
Each equation ends with a semicolon which, due to keypunch limita¬
tion, is represented by a period followed by a comma. An example of
a syntax equation is:
LOGICAL VALUE = ‘. TRUE ’ / ‘. FALSE ’.,
In the versions of ALGOL described in this paper the symbols which
are usually printed in boldface type will begin with periods, for
example:
.PROCEDURE .TRUE .IF
To indicate that a syntactic element is optional, it may be put in
alternation with the word . EMPTY. For example:
SUBSECONDARY = ‘ * ’ PRIMARY / . EMPTY . ,
SECONDARY = PRIMARY SUBSECONDARY . ,
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By factoring, these two equations can be written as a single equation.
SECONDARY = PRIMARY (‘ * ’ PRIMARY / . EMPTY).,
Built into the META II language is the ability to recognize three
symbols which are:
1. Identifiers - represented by . ID,
2. Strings - represented by . STRING,
3. Numbers — represented by . NUMBER.
The definition of identifier is the same in META II as in ALGOL,
viz., a letter followed by a sequence of letters or digits. The definition
of a string is changed because of the limited character set available on
the usual keypunch. In ALGOL, strings are surrounded by opening and
closing quotation marks, making it possible to have quotes within a
string. The single quotation mark on the keypunch is unique, imposing
the restriction that a string in quotes can contain no other quotation
marks.
The definition of number has been radically changed. The reason
for this is to cut down on the space required by the machine subroutine
which recognizes numbers. A number is considered to be a string of
dijpts which may include imbedded periods, but may not begin or end
with a period; moreover, periods may not be adjacent. The use of the
subscript 10 has been eliminated.
Now we have enough of the syntax defining features of the
META II language so that we can consider a simple example in some
detail.
The example given here is a set of four syntax equations for defining
a very limited class of algebraic expressions. The two operators,
addition and multiplication, will be represented by + and * respectively.
Multiplication takes precedence over addition; otherwise precedence is
indicated by parentheses. Some examples are:
A
A + B
A + B *C
(A + B) * C
The syntax equations which define this class of expressions are as
follows:
EX3 = . ID / ‘ (‘ EX1 ’) ’.,
EX2 = EX3 ( * * * EX2 / . EMPTY ). ,
EX1 = EX2 ( ‘ + ’ EX1 / . EMPTY ). ,
EX is an abbreviation for expression. The last equation, which
defines an expression of order 1, is considered the main equation.
The equations are read in this manner. An expression of order 3 is
defined as an identifier or an open parenthesis followed by an expres¬
sion of order 1 followed by a closed parenthesis. An expression of
order 2 is defined as an expression of order 3, which may be followed
by a star which is followed by an expression of order 2. An expression
of order 1 is defined as an expression of order 2, which may be fol¬
lowed by a plus which is followed by an expression of order 1.
Although sequences can be defined recursively, it is more con¬
venient and efficient to have a special operator for this purpose. For
example, we can define a sequence of the letter A as follows:
SEQA = $ ‘ A ’.,
The equations given previously are rewritten using the sequence
operator as follows:
EX3 = . ID / ‘ (‘ EX1
EX2 = EX3 $ (‘ * ’ EX3 ) .,
EX1 = EX2 $ (‘ + ’ EX2 ).,
Output
Up to this point we have considered the notation in META II which
describes object language syntax. To produce a compiler, output
commands are inserted into the syntax equations. Output from a
compiler written in META II is always in an assembly language, but not
in the assembly language for the 1401. It is for an interpreter, such as
the interpreter I call the META II machine, which is used for all
compilers, or the interpreters I call the VALGOLI and VALGOLII
machines, which obviously are used with their respective source
languages. Each machine requires its own assembler, but the main
difference between the assemblers is the operation code table. Constant
codes and declarations may also be different. These assemblers all have
the same format, which is shown below.
LABEL CODE ADDRESS
1- -6 8- -10 12- -70
An assembly language record contains either a label or an op code of
up to 3 characters, but never both. A label begins in column 1 and may
extend as far as column 70. If a record contains an op code, then
column 1 must be blank. Thus labels may be any length and are not
attached to instructions, but occur between instructions.
To produce output beginning in the op code field, we write .OUT
and then surround the information to be reproduced with parentheses.
A string is used for literal output and an asterisk to output the special
symbol just found in the input. This is illustrated as follows:
EX3 = . ID . OUT (‘ LD ’ * ) / ‘ (‘ EX1 ’) ’.,
EX2 = EX3 $ (‘ * ’ EX3 . OUT ( ‘ MLT ’) ) . ,
EX1 = EX2 $ (‘+’EX2 .OUT(‘ADD’)) . ,
To cause output in the label field we write .LABEL followed by
the item to be output. For example, if we want to test for an identifier
and output it in the label field we write:
.ID .LABEL *
The META II compiler can generate labels of the form A01, A02,
A03, ... A99, B01, ... .To cause such a label to be generated, one
uses *1 or *2. The first time *1 is referred to in any syntax equation,
a label will be generated and assigned to it. This same label is output
whenever * 1 is referred to within that execution of the equation. The
symbol *2 works in the same way. Thus a maximum of two different
labels may be generated for each execution of any equation. Repeated
executions, whether recursive or externally initiated, result in a
continued sequence of generated labels. Thus all syntax equations
contribute to the one sequence. A typical example in which labels are
generated for branch commands is now given.
IFSTATEMENT = ‘. IF ’ EXP ‘ .THEN ’ .OUT (' BFP ’ *1)
STATEMENT ‘ .ELSE ’ .OUT ( ‘ B ’ *2 ) .LABEL *1
STATEMENT .LABEL *2 .,
The opcodes BFP and B are orders of the VALGOLI machine, and
stand for “branch false and pop” and “branch” respectively. The
equation also contains references to two other equations which are not
explicitly given, viz., EXP and STATEMENT.
VALGOL I — A Simple Compiler Written in META II
Now we are ready for an example of a compiler written in META II.
VALGOL I is an extremely simple language, based on ALGOL 60,
which has been designed to illustrate the META II compiler.
The basic information about VALGOL I is given in figure 1 (the
VALGOL I compiler written in META II) and figure 2 (order list of
the VALGOL I machine). A sample program is given in figure 3. After
each line of the program, the VALGOL I commands which the
compiler produces from that line are shown, as well as the absolute
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Number 44
143
interpretive language produced by the assembler. Figure 4 is output
from the sample program. Let us study the compiler written in
META II (figure 1) in more detail.
The identifier PROGRAM on the first line indicates that this is the
main equation, and that control goes there first. The equation for
PRIMARY is similar to that of EX3 in our previous example, but here
numbers are recognized and reproduced with a “load literal” command.
TERM is what was previously EX2; and EXP1 what was previously EX1
except for recognizing minus for subtraction. The equation EXP
defines the relational operator “equal,” which produces a value of 0
or 1 by making a comparison. Notice that this is handled just like the
arithmetic operators but with a lower precedence. The conditional
branch commands, “branch true and pop” and “branch false and pop,”
which are produced by the equations defining UNTILST and
CONDITIONALST respectively, will test the top item in the stack and
branch accordingly.
The “assignment statement” defined by the equation for
ASSIGNST is reversed from the convention in ALGOL 60, i.e., the
location into which the computed value is to be stored is on the right.
Notice also that the equal sign is used for the assignment statement and
that period equal (.=) is used for the relation discussed above. This is
because assignment statements are more numerous in typical programs
than equal compares, and so the simpler representation is chosen for
the more frequently occurring.
The omission of statement labels from the VALGOL I and
VALGOL II seems strange to most programmers. This was not done be¬
cause of any difficulty in their implementation, but because of a dislike
for statement labels on the part of the author. I have programmed
for several years without using a single label, so I know that they are
superfluous from a practical, as well as from a theoretical, standpoint.
Nevertheless, it would be too much of a digression to try to justify
this point here. The “until statement” has been added to facilitate
writing loops without labels.
The “conditional” statement is similar to the one in ALGOL 60,
but here the “else” clause is required.
The equation for “input/output,” IOST, involves two commands,
“edit” and “print.” The words EDIT and PRINT do not begin with
periods so that they will look like subroutines written in code. “EDIT”
copies the given string into the print area, with the first character in the
print position whish is computed from the given expression. “PRINT”
will print the current contents of the print area and then clear it to
blanks. Giving a print command without previous edit commands
results in writing a blank line.
IDSEQ1 and IDSEQ are given to simplify the syntax equation
for DEC (declaration). Notice in the definition of DEC that a branch
is given around the data.
From the definition of BLOCK it can be seen that what is con¬
sidered a compound statement in ALGOL 60 is, in VALGOL I, a
special case of a block which has no declaration.
In the definition of statement, the test for an IOST precedes that
for an ASSIGNST. This is necessary, because if this were not done the
words PRINT and EDIT would be mistaken as identifiers and the com¬
piler would try to translate “input/output” statements as if they were
“assignment” statements.
Notice that a PROGRAM is a block and that a standard set of
commands is output after each program. The “halt” command causes
the machine to stop on reaching the end of the outermost block,
which is the program. The operation code SP is generated after the
“halt” command. This is a completely 1401-oriented code, which
serves to set a word mark at the end of the program. It would not be
used if VALGOL I were implemented on a fixed word-length machine.
How the META II Compiler Was Written
Now we come to the most interesting part of this project, and
consider how the META II compiler was written in its own language.
The interpreter called the META II machine is not a much longer
1401 program than the VALGOL I machine. The syntax equations
for META II (figure 5) are fewer in number than those for the
VALGOL I machine (figure 1).
The META II compiler, which is an interpretive program from
the META II Machine, takes the syntax equations given in figure 5
and produces an assembly language version of this same interpretive
program. Of course, to get this started, I had to write the first compiler¬
writing compiler by hand. After the program was running, it could
produce the same program as written by hand. Someone always asks
if the compiler really produced exactly the program I had written
by hand and I have to say that it was “almost” the same program.
I followed the syntax equations and tried to write just what the
compiler was going to produce. Unfortunately I forgot one of the re¬
dundant instructions, so the results were not quite the same. Of course,
when the first machine-produced compiler compiled itself the second
time, it reproduced itself exactly.
The compiler originally written by hand was for a language called
META I. This was used to implement the improved compiler for META
II. Sometimes, when I wanted to change the metalanguage, I could
not describe the new metalanguage directly in the current metalan¬
guage. Then an intermediate language was created-one which could
be described in the current language and in which the new language
could be described. I thought that it might sometimes be necessary to
modify the assembly language output, but it seems that it is always
possible to avoid this with the intermediate language.
The order list of the META II machine is given in figure 6.
All subroutines in META II programs are recursive. When the pro¬
gram enters a subroutine a stack is pushed down by three cells. One cell
is for the exit address and the other two are for labels which may be
generated during the execution of the subroutine. There is a switch
which may be set or reset by the instructions which refer to the input
string, and this is the switch referred to by the conditional branch
commands.
The first thing in any META II machine program is the address
of the first instruction. During the initialization for the interpreter,
this address is placed into the instruction counter.
VALGOL II Written in META II
VALGOL II is an expansion of VALGOL I, and serves as an il¬
lustration of a fairly elaborate programming language implemented in
the META II system. There are several features in the VALGOL II
machine which were not present in the VALGOL I machine, and which
require some explanation. In the VALGOL II Machine, addresses as
well as numbers are put in the stack. They are marked appropriately
so that they can be distinguished at execution time.
The main reason that addresses are allowed in the stack is that,
in the case of a subscripted variable, an address is the result of a com¬
putation. In an assignment statement each left member is compiled into
a sequence of code which leaves an address on top of the stack. This is
done for simple variables as well as subscripted variables, because the
philosophy of this compiler writing system has been to compile every¬
thing in the most general way. A variable, simple or subcripted, is
always compiled into a sequence of instructions which leaves an address
on top of the stack. The address is not replaced by its contents until
the actual value of the variable is needed, as in an arithmetic expression.
A formal parameter of a procedure is stored either as an address or
as a value which is computed when the procedure is called. It is up to
the load command to go through any number of indirect address in
order to place the address of a number onto the stack. An argument of
a procedure is always an algebraic expression. In case this expression is
a variable, the value of the formal parameter will be an address com¬
puted upon entering the procedure.
The operation of the load command is now described. It causes
the given address to be put on top of the stack. If the content of this
top item happens to be another address, then it is replaced by that
other address. This continues until the top item on the stack is the
address of something which is not an address. This allows for formal
parameters to refer to other formal parameters to any depth.
No distinction is made between integer and real numbers. An in¬
teger is just a real number whose digits right of the decimal point are
zero. Variables initially have a value called “undefined,” and any
attempt to use this value will be indicated as an error.
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An assignment statement consists of any number of left parts
followed by a right part. For each left part there is compiled a sequence
of commands which puts an address on top of the stack. The right part
is compiled into a sequence of instructions which leaves on top of the
stack either a number or the address of a number. Following the in¬
struction for the right part there is a sequence of store commands, one
for each left part. The first command of this sequence is “save and
store,” and the rest are “plain” store commands. The “save and store”
puts title number which is on the top of the stack (or which is referred
to by the address on top of the stack) into a register called SAVE.
It then stores the contents of SAVE in the address which is held in the
next to top position of the stack. Finally it pops the top two items,
which it has used, out of the stack. The number, however, remains in
SAVE for use by the following store commands. Most assignment
statements have only one left part, so “plain” store commands are
seldom produced, with the result that the number put in SAVE is
seldom used again.
The method for calling a procedure can be explained by reference
to illustrations 1 and 2. The arguments which are in the stack are
moved to their place at the top of the procedure. If the number of
xxxxxxxx
Function
xxxxxxxx
xxxxxxxx
Arguments
xxxxxxxx
b
Word of one blank character
the end of the arguments.
to mark
Body. Branch commands cause control
to go around data stored in this area.
Ends with a “return” command.
Illustration 1
Storage Map for VALGOL II Procedures
XXXXXXXX
XXXXXXXX
Arguments in reverse order
xxxxxxxx
XXX
XXX
Flag
Address of Exit
procedure
XXX
Stack before executing Stack after executing
the call instruction the call instruction
Illustration 2
Map of the Stack Relating to Procedure Calls
arguments in the stack does not correspond to the number of arguments
in the procedure, an error is indicated. The “flag” in the stack works
like this. In the VALGOL II machine there is a flag register. To set a
flag in the stack, the contents of this register is put on top of the stack,
then the address of the word above the top of the stack is put into the
flag register. Initially, and whenever there are no flags in the stack, the
flag register contains blanks. At other times it contains the address of
the word in the stack which is just above the uppermost flag. Just be¬
fore a call instruction is executed, the flag register contains the address
of the word in the stack which is two above the word containing the
address of the procedure to be executed. The call instruction picks up
the arguments from the stack, beginning with the one stored just above
the flag, and continuing to the top of the stack. Arguments are moved
into the appropriate places at the top of the procedure being called.
An error message is given if the number of arguments in the stack does
not correspond to the number of places in the procedure. Finally the
old flag address, which is just below the procedure address in the stack,
is put in the flag register. The exit address replaces the address of the
procedure in the stack, and all the arguments, as well as the flag, are
popped out. There are just two op codes which affect the flag register.
The code “load flag” puts a flag into the stack, and the code “call”
takes one out.
The library function “WHOLE” truncates a real number. It does
not convert a real number to an integer, because no distinction is
made between them. It is substituted for the recommended function
‘ENTIER” primarily because truncation takes fewer machine instruc¬
tions to implement. Also, truncation seems to be used more frequently.
The procedure ENTIER can be defined in VALGOL II as follows:
.PROCEDURE ENTIER(X) .,
.IF 0 .L = X .THEN X .ELSE
IF WHOLE(X) = X .THEN X .ELSE
WHOLE(X) -1
The “for statement” in VALGOL II is not the same as it is in
ALGOL. Exactly one list element is required. The “step ... until”
portion of the element is mandatory, but the “while” portion may
be added to terminate the loop immediately upon some condition.
The iteration continues so long as the value of the variable is less than
or equal to the maximum, irrespective of the sign of the increment.
Illustration 3 is an example of a typical “for statement.” A flow chart
of this statement is given in illustration 4.
.FOR I = 0 .STEP 1 .UNTIL N .DO
[statement]
SET
Set switch to indicate first time through.
A91
LD
1
FLP
]
Test for first time through.
BFP
A92 J
LDL
0 1
SST
i Initialize variable.
B
A93 )
A92
LDL
1 )
Increment variable.
’
ADS
1
A93
RSR
1
Compare variable to maximum.
LD
N
LEQ
BFP
A94 J
[statement]
RST
Reset switch to indicate not first time
through.
B A91
A94
Illustration 3
Compilation of a typical “for statement”
in VALGOL II
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Number 44
145
It can back-up the input and output and return false. The advantages
of backup are as follows:
Illustration 4
Flow chart of the “for statement”
given in figure 12
Figure 7 is a listing of the VALGOLII compiler written in META II.
Figure 8 gives the order list of the VALGOL II machine. A sample
program to take a determinant is given in figure 9.
Backup vs. No Backup
Suppose that, upon entry to a recursive subroutine, which repre¬
sents some syntax equation, the positions of the input and output
are saved. When some non-first term of a component is not found, the
compiler does not have to stop with an indication of a syntax error.
1. It is possible to describe languages, using backup, which cannot be
described without backup.
2. Even for a language which can be described without backup, the
syntax equations can often be simplified when backup is allowed.
The advantages claimed for non-backup are as follows:
1. Syntax analysis is faster.
2. It is possible to tell whether syntax equations will work just by
examining them, without following through numerous examples.
The fact that rather sophisticated languages such as ALGOL and
COBOL can be implemented without backup is pointed out by various
people, including Conway, 5 and they are aware of the speed advant¬
ages of so doing. I have seen no mention of the second advantage of
no-backup, so I will explain this in more detail.
Basically one writes alternations in which each term begins with
a different symbol. Then it is not possible for the compiler to go down
the wrong path. This is made more complicated because of the use of
“.EMPTY”. An optional item can never be followed by something that
begins with the same symbol it begins with.
The method described above is not the only way in which backup
can be handled. Variations are worth considering, as a way may be
found to have the advantages of both backup and no-backup.
Further Development of META Languages
As mentioned earlier, META II is not presented as a standard
language, but as a point of departure from which a user may develop
his own META language. The term “META Language,” with “META”
in capital letters, is used to denote any compiler-writing language so
developed.
The language which Schmidt 1 implemented on the PDP-1 was
based on META 1. He has now implemented an improved version of
this language for a Beckman machine.
Rutman 9 has implemented LOGIK, a compiler for bit-time simula¬
tion, on the 7090. He uses a META Language to compile Boolean
expressions into efficient machine code. Schneider and Johnson 10
have implemented META 3 on the IBM 7094, with the goal of pro¬
ducing an ALGOL compiler which generates efficient machine code.
They are planning a META langauge which will be suitable for any
block structured language. To this compiler-writing language they give
the name META 4 (pronounced metaphor).
References
1. Schmidt, L., “Implementation of a Symbol Manipulator for Heuristic
Translation,” 1963 ACM Natl. Conf., Denver, Colo.
2. Metcalfe, Howard, “A Parameterized Compiler Based on Mechan¬
ical Linguistics,” 1963 ACM Natl. Conf., Denver, Colo.
3. Schorre, Val, “A Syntax-Directed SMALGOL for the 1401,”
1963 ACM Natl. Conf., Denver, Colo.
4. Glennie, A., “On the Syntax Machine and the Construction of a
Universal Compiler,” Tech. Report No. 2, Contract NR 049-141,
Carnegie Inst, of Tech., July, 1960.
5. Conway, Melvin E., “Design of a Separable Transition-Diagram
Compiler,” Comm. ACM, July 1963.
6. Irons, E.T., The Structure and Use of the Syntax-Directed Com¬
piler,” Annual Review in Automatic Programming, The Macmillan
Co., New York.
7. Bastian, Lewis, “A Phrase-Structured Language Translator,”
AFCRL- Rept-62-549, Aug. 1962.
8. Chomsky, Noam, “Syntax Structures,” Mouton and Co., Publishers,
The Hague, Netherlands.
9. Rutman, Roger, “LOGIK, A Syntax Directed Compiler for Com¬
puter Bit-Time Simulation,” Master Thesis, UCLA, August 1964.
lO.Schneider, F.W., and G.D. Johnson, “A Syntax-Directed Com¬
piler-Writing Compiler to Generate Efficient Code,” 1964 ACM
Natl. Conf., Philadelphia.
Number 44
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Dr. Dobb's Journal of Computer Calisthenics 8t Orthodontia, Box E. Menlo Park, CA 94025
Page 21
THE VALGOL 1 COMPILER WRITTEN IN META II LANGUAGE
FIGURE 1
A PROGRAM AS COMPILED FOR TmE VALGOL I MACHINE
FIGURE 3
•SYNTAX PROGRAM
PRIMARY - .10 .OUTf'LO • *> /
• NUMBER «OUT(*LOL* •! /
•t• EXP •)• ••
TERM - PRIMARY *(••• PRIMARY •OUTCMLT*! I ••
EXP1 • TERM *!•♦• TERM .OUT!•ADD*I /
TERM .OUT(•SUB*I ) ••
EXP - EXP1 I •.-• EXP 1 «OUTI•EQU'I / .EMPTY) ••
ASSIGNST - EXP .ID .OUTMST • •) ..
UNTILST • ••UNTIL' .LABEL •! EXP '.DO* .OUTI'BTP* *21
ST .OUT(*8 ' *1) .LABEL *2 ••
CONDITIONALST - '•IF* EXP '.THEN' .OUTt'BFP* «1|
ST '.ELSE* .OUT I•8 • *2) .LABEL «1
ST .LABEL *2 ••
IOST - 'EDIT* EXP .STRING
•OUT(•EOT• *> •)• /
•PRINT' .OUT I * PNT•I •»
I0SE01 - .ID .LABEL • .OUTI'BLK 1*1 ••
IOSEQ • IDSE01 *('•• I0SE01) ••
DEC • '.REAL* .OUTI•B • *1) IDSEO .LABEL *1 ••
BLOCK - ••BEGIN* IDEC *••* / .EMPTY)
ST *(•.»• ST) '.END* .i
ST - IOST / ASSIGNST / UNTILST /
CONDITIONALST / BLOCK ••
PROGRAM - BLOCK .OUTI'HLTO
•OUT I•SP 1•) .OUT I'END*) ..
• BEGIN
.REAL X •• 0 - X .»
B A01
X
BLK 001
A01
LOL C
ST K
•UNTIL X .« 3 .00 .BEGIN
A02
LO X
LOL 3
SOU
BTP A53
EDIT! X«X * 10 ♦ I.
LO X
LO X
MLT
LDl 10
MLT
LDL 1
ADO
EOT 01'*'
PNT
LD X
LDL 0.1
ADO
ST X
0000 G 0012
0004
0004
0012
0012 A
0021 B 0004
0023
0025 0 CO04
002* A
00’£ c
0029 K 0047
PR.INT ..X*0.1*X
00*3 O 00C4
0047 0 OC r -4
OOtl Z
00! c A
00B1 E
OC62 A
0071 C
0072 I
00 74 0
0075 0 0004
0077 A
0085 C
0087 o 0004
0093 G 0C25
0097
OROER LIST OF THE VALGOL 1 MACHINE
FIGURE 2
OUTPUT FROM TME VALGOL I PROGRAM GIVEN IN FIGURE 3
FIGURE 4
MACHINE COOES
LDL NUMBER LOAO LITERAL
ST AAA STORE
ADO ADD
SUB SUBTRACT
MLT MULTIPLY
EQU EQUAL
8 AAA BRANCH
BFP AAA BRANCH FALSE
AND POP
BTP AAA BRANCH TRUE
AND POP
EOT STRING EDIT
PUT THE CONTENTS OF THE ADDRESS AAA
ON TOP OF THE STACK.
PUT THE GIVEN' NUMBER ON TOP OF
THE STACK.
STORE THE NUMBER WHICH IS ON TOP
OF THE STACK INTO THE AODRESS AA*
AND POP UP TME STACK.
REPLACE THE TWO NUMBERS WHICH ARE
ON TOP OF THE STACK WITH THEIR
SUM.
SUBTRACT TME NUMBER WHICH IS ON
TOP OF THE STACK FROM TME NUMBER
WHICH IS NEXT TO THE TOP. THEN
REPLACE THEM By THIS DIFFERENCE.
REPLACE THE TWO NUMBERS WHICH ARE
ON TOP OF THE STACK WITH THEIR
PRODUCT.
COMPARE THE TWO NUMBERS ON TOP OF
TME STACK. REPLACE THEM BY THE
INTEGER 1. IF THEY ARC EQUAL. OR BY
THE INTEGER 0. IF THEY ARE UNEQUAL.
BRANCH TO THE ADORESS AAA.
BRANCH TO THE ADDRESS AAA IF THE
TOP TERM IN TME STACK IS THE
INTEGER 0. OTHERWISE. CONTINUE
IN SEQUENCE. IN EITHER CASE.
POP UP TME STACK.
BRANCH TO THE AODRESS AAA IF THE
TOP TERM IN THE STACK IS NOT THE
INTEGER 0. OTHERWISE. CONTINUE
IN SEQUENCE. IN EITHER CASE.
POP UP THE STACK.
RO0ND THE NUMBER WHICH IS ON TOP OF
THE STACK TO THE NEAREST INTEGER N.
HOVE THE 6IVEN STRING INTO THE
PRINT AREA SO THAT ITS FIRST CHAR¬
ACTER FALLS ON PRINT POSITION N.
IN CASE THIS WOULO CAUSE CHARACTERS
TO FALL OUTSIDE THE PRINT AREA. NO
MOVEMENT TAKES PLACE.
PRINT A LINE. THEN SPACE AND CLEAR
THE PRINT AREA.
HALT HALT.
CONSTANT ANO CONTROL CODES
BLK NNN BLOCK
N - 1—9. CONSTANT COOE PRODUCING
N BLANK SPACES.
PROOUCES A BLOCK OF NNN EIGHT
CHARACTER WORDS.
DENOTES THE ENO OF THE PROGRAM.
THE META II COMPILER WRITTEN IN ITS OWN LANGUAGE
FIGURE 5
OUT 1 • ••!• .OUTI'GNl'l / »»2* .OUT<*£>N2»J /
••• .OUT(•Cl*) / .STRING .OUT(*CL • *)..
OUTPU ' - I•.CUT• 'I*
* OUT1 •»» / •.LABEL• •OUTI'LB*) 0071! .OUTf'OUT') ••
EX3 • .ID .OUT ( »CLL» •> / .STRING
• OUTI • TST • *) / • • ID• .OUTCMD'I '
•.NUMBER* .OUT*'NUN') /
••STRING* .OUTC•SR•1 / •!• EXl •)• /
••EMPTY* .OUT!'SET*) /
•*• ..LABEL *1 EX3
.OUT I'BT • *11 .OUT I'SET•1•.
EX2 - (EX3 .OUT(•8F • •!» / OUTPUT >
SCEX3 .OUT(•BE'I ✓ OUTPUT)
.LABEL *1 ••
EXl - EX2 SC'/' .OUTI'BT • *1) EX2 I
•LABEL *1 ••
ST ■ .ID .LABEL •
'.»• .OUT I*R•)••
PROGRAM - '.SYNTAX' .ID .OUT!'ADR* •)
S ST '.END* .OUT(•END*I•»
Page 22
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
ORDER LIST OF THE META II MACHINE
FIGURE 6
MACHINE COOES
TST STRING TEST AFTER DELETING INITIAL BLANKS IN
THE INPUT STRING* COMPARE IT TO THE
STRING GIVEN AS ARGUMENT* IF THE
COMPARISON IS MET. OELETE THE
MATCHED PORTION FROM THE INPUT AND
SET SWITCH. IF NOT MET. RESET
SWITCH.
ID IDENTIFIER AFTER DELETING INITIAL BLANKS IN
THE INPUT STRING. TEST IF IT BEGINS
WITH AN IDENTIFIER. IE.. A LETTER
FOLLOWED BY A SEOUENCE OF LETTERS
AND/OR DIGITS. IF SO. DELETE THE
IDENTIFIER AND SET SWITCH. IF NOT.
RESET SWITCH.
NUM NUMBER AFTER DELETING INITIAL BLANKS IN
THE INPUT STRING, TEST IF IT BEGINS
WITH A NUMBER. A NUMBER IS A
STRING CF DIGITS WHICH MAY CONTAIN
IM3EDED PERIODS. BUT MAY NOT BEGIN
OR EnD WITH A PER 100. MOREOVER. NO
TWO PERIODS MAY BE NEXT TO ONE
ANG r *ER. IF A NUMBER IS FOUND.
DELETE IT AND SET SWITCH. IF NOT.
RESET SWITCH.
SR STRING AFTER DELETING INITIAL BLANKS IN
THE INPUT STRING, TEST IF IT BEGINS
WITH a STRING. IE., A SINGLE OUOTE
FOulCwED BY A SEOUENCE OF ANY
CHARACTERS OTHER THAN SINGLE QUOTE
FOLLOWED BY ANOTHER SINGLE QUOTE.
! r A s’RInG IS FOUND. DELETE IT AND
SET Sw!?Cn. IF NOT. RESET SWITCH.
CLL AAA CALL E*'THE SUBROUTINE BEGINNING IN
wDCAMGm aAa. if THE TOP TWO TERMS
OF the STACK ARE BLANK, PUSH THE
STACK DOWS B" ONE CELL. OTHERWISE.
PUSH IT down 8y THREE CELLS. SET A
FLAG IN The stack TO INOICATE
V"ETHE* IT h-*S BEEN PUSHED BY ONE
CR ThPEE CELLS. THIS FLAG ANO THE
EXIT ADDRESS GO INTO THE THIRD
CELw CLEAR THE TOP TWO CELLS TO
FLANKS TO INDICATE THAT THEY CAN
ACCEPT ADDRESSES WHICH MAY BE
GENERATED WITHIN ThE SUBROUTINE.
Pigure 6.1
R RETURN RETURN TO THE EXIT ADDRESS. POPPING
UP THE STACK BY ONE OR THREE CELLS
ACCORDING TO THE FLAG. IF THE
STACK IS POPPED BY ONLY ONE CELL.
THEN CLEAR THE TOP TWO CELLS TO
BLANKS. BECAUSE * HeY WERE BLANK
WHEN THE SUBROUTINE WAS ENTEREO.
SET SET SET BRANCH SWITCH ON.
B AAA BRANCH BRANCH UNCONDITIONALLY TO LOCATION
AAA.
BT AAA BRANCH IF TRUE BRANCH TO LOCATION AAA IF SWITCH IS
ON. OTHERWISE. CONTINUE IN SEQ¬
UENCE.
BF AAA BRANCH IF FALSE BRANCH TO LOCATION AAA IF SWITCH
IS OFF. OTHERWISE. CONTINUE IN
SEOUENCE.
BE BRANCH TO ERROR HALT IF SWITCH IS OFF, OTHERWISE.
IF FALSE CONTINUE IN SEOUENCE.
CL STRING COPY LITERAL OUTPUT THE VARIABLE LENGTH STRING
GIVEN AS THE ARGUMENT. A BLANK
CHARACTER WILL BE INSERTED IN THE
OUTPUT FOLLOWING THE STRING.
Cl COPY INPUT OUTPUT THE LAST SEOUENCE OF CHAR¬
ACTERS DELETED FROM THE INPUT
STRING. THIS COMMAND MAY NOT FUNC¬
TION PROPERLY IF THE LAST COMMAND
WHICH COULD CAUSE DELETION FAILED
TO DO SO.
GNl GENERATE 1 THIS CONCERNS THE CURRENT LABEL 1
CELL. IE.. THE NEXT TO TOP CELL IN
THE STACK. WHICH IS EITHER CLEAR OR
CONTAINS A GENERATED LABEL. IF
CLEAR. GENERATE A LABEL AND PUT IT
INTO THAT CELL. WHETHER THE LABEL
MAS JUST BEEN PUT INTO THE CELL OR
WAS ALREADY THERE. OUTPUT IT.
FINALLY, INSERT A Bt.AMK CHARACTER
IN THE OUTPUT FOLLOWING THE LABEL.
GN2 GENERATE 2 SAME AS GNU EXCEPT THAT IT CON¬
CERNS THE CURRENT LABEL 2 CELL.
IE., THE TOP CELL IN THE STACK.
LB LABEL SET THE OUTPUT COUNTER TO CARO
COLUMN 1.
OUT OUTPUT PUNCH CARD AND RESET OUTPUT COUNTER
TO CARD COLUMN 8.
Figure 6.2
CONSTANT AND CONTROL CODES
ADR IDENT ADDRESS PROOUCES THE ADDRESS WHICH IS
ASSIGNED TO THE GIVEN IDENTIFIER AS
A CONSTANT.
END END DENOTES THE ENO OF THE PROGRAM.
Figure 6.3
VALGOL II COMPILER WRITTEN IN META II
FIGURE 7
•SYNTAX PROGRAM
ARRAYPART - •(.' EXP •#»• .OUT('AIA') ••
CALLPART - • « • .OUT ( ' IDF • ) IEXP »('.' EXP) /
•Emptyi .outmcll') ••
VARIABLE • .ID .OUTI'LO • *) I ARRAYPART / .EMPTY! «•
PRIMARY - ‘WHOLE' •!» EXP •)» .OUTt'WHL'l /
•ID .OUT(•LO • •) (ARRAYPART / CALLPART / -EMPTY) /
'.TRUE* .OUT1 1 SET•) / '.FALSE' .OUTI'RSTM /
•0 • .OUT(•RST•I / *1 ' .OUT('SET') /
•NUMBER .OUTI'LDL* *) /
•I* EXP •)• .»
TERM • PRIMARY * I'*' PRIMARY .OUTI'MLT't /
•/• PRIMARY .OUTI•DIV•) /
'•/.' PRIMARY .OUT('DIV') .OUT('WHL') ) •*
EXP2 - •-• TERM .OUTI'NEG'I /
TERM / TERM ..
EXP1 - EXP2 *!•♦' TERM .OUT('ADD') /
TERM .OUT(•SUB•11 ••
RELATION ■ EXP 1 I
•.L»* EXPl .OUT I'LEO•) /
'.L' EXP 1 .OUT('LES') /
EXPl .OUT('EQU') t
EXPl .OUT('EOU') .OUT('NOT•) t
'.G-* EXPl .OUT('LES') .OUT('NOT') /
•.G* EXPl .OUT!'LEO') .OUTI'NOT'I /
•EMPTY) ..
BPR1MARY - ••-' RELATION .OUT('NOT') /
RELATION ••
STERN • BPRIMARY S <••„' .OUTI'BF • *1)
.OUT('POP') BPRIMARY)
•LABEL *1 «•
BEXPl - BTERM At '.V' .OUTCBT • *11
•OUT(•POP•) BTERM)
•LABEL *1 ••
IMPLICATION! ■ '.IMP' .OUT('NOT')
• OUT I • BT • Ml .OUTt'POP')
BEXPl .LABEL M ..
IMPLICATION - BEXPl % IMPLICATION! ••
Figure 7.1
EOUlV - IMPLICATION tC.EO' .OUT('EOU') ) •*
EXP - '.IF* EXP '.THEN* .OOTI'BFP' *1)
EXP .OUTl'B • *2) .LABEL *1
'.ELSE* EXP .LABEL "2 ✓
EOUIV .•
ASSIGNPART • '•' EXP I ASSIGNPART .OUT!'ST*I /
•EMPTY .OUTI'SST') ) ..
ASSIGNCALLST • .10 .OUTCLD • •) (ARRAYPART ASSIGNPART /
ASSIGNPART / (CALLPART / .EMPTY
• OUTOLDF'I .OUT!'CLL* ) I
•OUT('POP') ) •»
UNTILST • '.UNTIL* .LABEL M EXP
'.DO* .OUTI'BTP' Ml ST
•OUT('B ' *1) .LABEL *2 ••
WMILECLAUSE « '.WHILE' .OUT (• BF ' M)
.OUT('POP') EXP .LABEL »1 / .EMPTY ••
FORCLAUSE • VARIABLE '•« .OUTI'FLP'I
•OUT('BFP* *1) EXP '.STEP'
•OUT(•SST•) .OUTl'B • *2)
•LABEL M EXP '.UNTIL' .OUT('AOS')
•LABEL "2 .OUTI•RSR') EXP
•OUT('LEQ') WHILCCLAUSE '.DO* ••
FORST • '.FOR* .OUT!'SET') .LABEL M
FORCLAUSE .OUTC'BFP' *2) ST
•OUT!'RST') .OUTl'B • •!)
•LABEL M ••
IOCALL • 'READ' VARIABLE '.' EXP •)• .OUT('REO') /
•WRITE' VARIABLE EXP •»« .OUT('WRT') /
•EDIT' •I' EXP ••' .STRING
•Out i• edt' m •)• /
•PRINT' .OUTCPNT'I ✓
'EJECT* .OUTI'EJT'I ••
Number 44
148
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 23
IOSEQI . .ID .LABEL* .OUTC'BLK 1»> ••
IDSEQ • IOSEQI •(••• IOSEQI) ••
TYPEDEC - *.REAL* IDSEQ ..
APRAYl • .10 .LABEL * •(.• 'O' •••* .HUMBER
•OUTCBL^ l') .OUTI 'BLK' *> ••
ARRAYOEC - • .ARRAY* ARRAY 1 S( •*' ARRAY1) ••
PROCEDURE - ‘.PROCEDURE* .10 .LABEL *
•LABEL *1 .OUTC'BLK 1') 'I'
< IDSEQ / .EMPTY) *»• .OUTCSP l'l
ST .OUTI»R • *1) •*
^lgUTB 7*2
OEC • TYPEDEC / ARRAYOEC / PROCEDURE .«
BLOCK - '.BEGIN* .OUT(*8 • *1) StOEC '..')
.LABEL *1 it SC.*' STJ *.END'
(•ID / .EMPTY) ••
UNCONOITIONALST • IOCALL / ASSIGNCAU-ST /
BLOCK ..
CONDST - '.IF* f.XP '.THEN* .OUTCBFP* *1)
(UNCOHO!TIOHALST C.CLSS' .OUT('3 ' *2)
• LABEL *1 ST «LABEL S .EMPTY
• LABEL *i) / < C 0R$7 ,• UNTiLST)
•LABEL *1) .»
ST - CONCST / UHCOMOITIOHALST / FO«ST /
UNI I LSI / ■uMPTV ..
program - block
• OUT ( 'MLT * ) .OUTCSP 1') .OUT C END') . v
Figure 7.3
ORDER LIST OF THE VALGOL II MACHINE
FIGURE S
MACHINE CODES
L D AAA LOAD PUT THE ADORESS AAA OH TOP OF THE
STACK.
LDL HUMBER LOAD LITERAL PUT THE GIVEN HUMBER OH TOP OF
THE STACK.
SET SET PUT THE IHTEGER 1 ON TOP OF THE
STACK.
RST RESET PUT THE INTEGER 0 OH TOP OF THE
STACK.
ST STORE STORE THE CONTENTS OF THE REGISTER.
STACKl. IN THE ADORESS WHICH IS OH
TOP OF THE STACK. THEN POP UP THE
STACK.
ADD THE HUMBER OH TOP OF THE STACK
TO THE HUMBER WHOSE ADORESS IS NEXT
TO THE TOP. AND PLACE THE SUM IN
THE REGISTER. STACKl. THEN STORE
THE CONTENTS Or THAT REGISTER IN
THAT ADORESS. AND POP THE TOP TWO
ITEMS OUT OF THE STACK.
PUT THE HUMBER OH TOP OF THE STACK
INTO THE REGISTER. STACKl. THEN
STORE THE CONTENTS OF THAT REGISTER
IN THE ADORESS WHICH IS THE NEXT
TO TOP TERM OF THE STACK. THE TOP
TWO ITEMS ARE POPPED OUT OF THE
STACK.
RSR RESTORE PUT THE CONTENTS OF THE REGISTER.
STACKl. OH TOP OF THE STACK.
ADD ADO REPLACE THE TWO NUMBERS WHICH ARE
NOTE 2 OH TOP OF THE STACK WITH THEIR
SUM.
SUB SUBTRACT SUBTRACT THE HUMBER WHICH IS OH
NOTE 2 TOP OF THE STACK FROM THE HUMBER
WHICH IS NEXT TO THE TOP. THEN
REPLACE THEM BY THIS DIFFERENCE.
MLT MULTIPLY REPLACE THE TWO NUMBERS WHICH ARE
NOTE 2 ON TOP OF THE STACK WITH THEIR
PRODUCT.
DIV DIVIDE DIVIDE THE NUMBER WHICH IS NEXT TO
NOTE 2 THE TOP OF THE STACK BY THE NUMBER
WHICH IS ON TOP OF THE STACK. THEN
REPLACE THEM BY THIS OUOTIENT.
Figure 8.1
ADS ADO TO STORAGE
NOTE 1
SST SAVE ANO STORE
NOTE 1
NEG
WHL
NEGATE CHANGE THE SIGN OF THE NUMBER ON
NOTE 1 TOP OF THE STACK.
WHOLE TRUNCATE THE NUMBER WHICH IS ON
TOP OF THE STACK.
NOT IF THE TOP TERM IN THE STACK IS THE
INTEGER 0. THEN REPLACE IT WITH THE
INTEGER 1. OTHERWISE. REPLACE IT
WITH THE INTEGER 0.
LESS THAN OR EQUAL IF THE NUMBER WHICH IS NEXT TO
NOTE 2 THE TOP OF THE STACK IS LESS THAN
OR EQUAL TO THE HUMBER ON TOP OF
THE STACK. THEN REPLACE THEM WITH
THE INTEGER l. OTHERWISE. REPLACE
THEM WITH THE INTEGER 0.
LESS THAN
NOTE 2
EQU EQUAL
NOTE 2
B AAA BRANCH
BT AAA BRANCH TRUE
BF AAa -DRaMCM FALSE
BTP AAA BRANCH TRUE
AND POP
BFP AAA BRANCH FALSE
AND POP
EOT STRING EDIT
NOTE l
PNT
EJT
RED
PRINT
EJECT
READ
IF THE NUMBER WHICH IS NEXT TO
THE TOP OF THE STACK IS LESS THAN
THE NUMBER ON TOP OF THE STACK.
THEN REPLACE THEM WITH THE
INTEGER 1. OTHERWISE. REPLACE THEM
WITH THE INTEGER U.
COMPARE THE TWO NUMBERS ON TOP OF
THE STACK. REPLACE THEM BY THE
INTEGER 1. IF THEY ARE EOuAl. OR By
THE INTEGER 0. IF THEY ARE UNEQUAL.
BRANCH TO THE ADORESS AAA.
BRANCH TO THE ADDRESS AAA IF THE
TOP TERM IN THE STACK IS NOT THE
INTEGER G. OTHERWISE. CONTINUE
IN SEQUENCE. 00 NOT POP UP THE
STACK,
BRANCH TO THE ADDRESS AAA IF THE
TOP TERM IN THE STACK IS THE
iN EGcr! 0. OTHERWISE. CONTINUE
IN SEQUENCE. DO NOT POP UP THE
1 :ACK*
ESANCH TO Th£ ADDRESS AAA IF THE
TOP TERM IN THE STACK IS NOT THE
INTEGER 0. OTHERWISE. CONTINUE
IN SEQUENCE. IN EITHER CASE. POP
UP Tn£ ST'.CK.
60ANCW TO THE ADDRESS AAA IF THE
TOO TERM IN TH= STACK IS THE
INTEGER 0. OTHERWISE. CONTINUE
IN SEQUENCE• IN EITHER CASE*
POP UP THE STACK.
ARRAY INCREMENT
ADORESS
Figure 8.2
ENTER A PROCEOURE AT THE ADORESS
WHICH IS BELOW THE FLAG.
PUT THE ADDRESS WHICH IS IN THE
FLAG REGISTER ON TOP OF THE STACK.
ANO PUT THE ADORESS OF THE TOP OF
THE STACK INTO THE FLAG REGISTER.
RETURN FROM PROCEDURE.
INCREMENT THE ADDRESS WHICH IS NEXT
TO THE TOP OF THE STACK BY THE
INTEGER WHICH IS ON TOP OF THE
STACK, AND REPLACE THESE BY THE
RESULTING ADORESS.
INTERCHANGE THE TOP TWO TERMS OF
THE STACK.
POP UP THE STACK.
ROUND THE NUMBER WHICH IS ON TOP OF
THE STACK To THE NEAREST INTEGER N.
MOVE THE GIVEN STRING INTO THE
PRINT AREA SO THAT ITS FIRST CHAR¬
ACTER FALLS ON PRINT POSITION N.
IN CASE THIS WOULD CAUSE CHARACTERS
TO FALL OUTSIDE THE PRINT AREA. NO
MOVEMENT TAKES PLACE.
PRINT A LINE. THEN SPACE AND CLEAR
THE PRINT AREA.
POSITION THE PAPER IN THE PRINTER
TO THE TOP LINE OF THE NEXT PAGE.
READ THE FIRST N NUMBERS FROM A
CARD AND STORE THEM BEGINNING IN
THE ADDRESS WHICH IS NEXT TO
THE TOP OF THE STACK. THE INTEGER
N IS THE TOP TERM OF THE STACK.
POP OUT BOTH THE ADORESS ANO THE
INTEGER. CAROS ARE PUNCHED WITH UP
TO 10 EIGHT DIGIT NUMBERS. DECIMAL
POINT IS ASSUMED To BE IN THE
MIDDLE. AN 11-PUNCH OVER THE
RIGHTMOST DIGIT INDICATES A NEG¬
ATIVE NUMBER.
Pigure 8.3
Page 24
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
149
EXAMPLE PROGRAM IN VALGOL II
FIGURE 9
WRT WRITE PRINT A LINE OF N NUMBERS BEGINNING
IN THE AOORESS WHICH IS NEXT 10
THE TOP OF THE STACK. THE INTEGER
N IS THE TOP TERM OF THE STACK.
POP OUT BOTH THE ADDRESS AND THE
INTEGER. TWELVE CHARACTER POSI¬
TIONS are allowed for each number.
THERE ARE FOUR DIGITS BEFORE AND
FOUR DIGITS AFTER THE 0EC1MAL.
LEADING ZEROES IN FRONT OF THE
DECIMAL ARE CHANGED TO BLANKS.
IF THE NUMBER IS NEGATIVE. A MINUS
SIGN IS PRINTED IN THE POSITION
BEFORE THE FIRST NON-BLANK CHARACT¬
ER.
MLT HALT HALT.
SP N
BLK NNN
END
CONSTANT AND CONTROL CODES
SPACE H • 1—9. CONSTANT CODE PRODUCING
N BLANK SPACES.
BLOCK PRODUCES A BLOCK OF NNN EIGHT
CHARACTER WORDS.
END DENOTES THE ENO OF THE PROGRAM.
NOTE 1. IF THE TOP ITEM IN THE STACK IS AN ADDRESS. IT IS
REPLACED BY ITS CONTENTS BEFORE BEGINNING THIS
OPERATION.
NOTE 2. SAME AS NOTE 1. BUT APPLIES TO THE TOP TWO ITEMS.
Figure 8.4
•BEGIN
• PROCEDURE DETERMINANT I A. N) ..
•8EGIN
•PROCEDURE DUMPi) .»
•BEGIN
•REAL D ••
•FOR D - 0 .STEP 1 .UNTIL N-l .DO
WRITEIPATRIXI• N*D N) ••
PRINT
•END DUMP .•
.PROCEDURE ABS(X) ••
ABS - .IF 0 .L- X .THEN X .ELSE -X ••
•REAL PRODUCT. FACTOR. TEMP. R, I. J •»
PROOUCT - l .♦
•FOR R - 0 .STEP 1 .UNTIL N-2
• WHILE PRODUCT .— 0 .DO .BEGIN
I - R ..
•FOR J • R»1 .STEP 1 .UNTIL N-l .DO
• IF ABSC AI• N*I ♦ R .1 ) .L
ABS( A|. N•J ♦ R •I | .THEN
I - J •»
•IF AC. N*I ♦ R .1 .- 0 .THEN
PRODUCT • 0
• ELSE
•IF I R .THEN .BEGIN
PRODUCT - -PRODUCT ••
•FOR J • R .STEP 1 .UNTIL N-l .DO
•BEGIN
TEMP ■ AC. N*R ♦ J •) ..
AC. N*R ♦ J .1 ■ AC. N* 1 + J •! •
AC. N*I ♦ J - TEMP .END .ENO ••
TEMP • AC. N*R ♦ R .1 ••
.FOR I ■ RM .STEP 1 .UNTIL N-l .DO
•BEGIN
FACTOR • AC. N* I ♦ R .) / TEMP ..
•FOR J • R .STEP 1 .UNTIL N-l .DO
AC. N*I ♦ J •I ■ AC. N*I ♦ J •)
-FACTOR • AC. N*R ♦ J .1 ..
DUMP
•END .END ..
•FOR I - 0 .STEP 1 .UNTIL N-l .00
PROOUCT • PRODUCT • AC. N*I ♦ I •) ..
DETERMINANT « PRODUCT
• ENl- DETERMINANT ..
•REAL M. W. T .» .ARRAY MATRIX C. 0 •• 24 .) M
•UNTIL .FALSE .DO .BEGIN
EDI TCI. 'FIND DETERMINANT OF' I .» PRINT.. PRINT..
REAO'M. II .»
•FOR W * 0 .STEP 1 .UNTIL H-l .00 .BEGIN
READC MA CRIX C. M*w •)• Mi ..
WRITECMATRIX I. M*W •). Ml .END ••
PRINT •• T ■ DETERMINANT. CMATRIX. Ml ••
WRITECT. II .. PRINT.. PRINT .ENO
•END PROGRAM
Number 44
150
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 25
| A Northstar BASIC
L_Cross-Reference Tool
BY TITUS PURDIN
5901 JFK # 101
N. Little Rock, Arkansas 72116
In the course of two years of micro computing, I cannot
count the number of times friends and acquaintances have
offered me copies of programs they have written, only to be
disappointed because their BASIC and my BASIC were so
vastly different. In many cases, when the offered programs
were just too good to pass up, I have locked myself in the
study for an evening and made the necessary conversions. It
isn’t a job that I relish. And while I haven’t found an easy way
to accomplish it, I have developed, over time, some tools to
ease the burden.
This particular program accepts programs in BASIC on
Northstar disks and compiles cross-reference lists for all varia¬
bles, string variables, array variables, and line numbers. I have
found this to be a valuable assist when converting programs
from one BASIC to another and when compacting a program
by placing multiple statements on a single line. Additionally,
I have discovered that such lists, annotated with the purpose
of each variable, are excellent pieces of documentation.
This program is written in 8080 assembly language and
requires 13.4K of RAM to accommodate the program and the
table space. The program itself requires 1.64K, and 12K is
allocated for space in which to build the cross-reference
tables. This latter space is more than sufficient for the largest
programs I have. It could be reduced if necessary to save space
by changing the allocation in line 5090 and changing the byte
against which the high order byte of the address is compared
at line 0945 to agree with the space allocated.
The program is designed to run at 2A00H and use the I/O
and disk drivers currently in your Northstar DOS. References
to these drivers are contained in the EQU vectors at the
opening of the assembly language listing for ease in changing
them if your drivers or your COS are not standard.
The program creates four separate lists:
1. Variables
2. String variables
3. Array variables
4. Line # references
Each of these are supported as linear linked lists in alphabetic
soft order. The storage areas SYTOP, STTOP, ARTOP, and
NMTOP are the top pointers for these four lists, and the
marker BBH is used to mark the end of each of these lists.
SYTOP
STTOP
ARTOP
NMTOP
1 I
1 1
1 1
1 1
T
T
T
list of
list of
list of
list of line
variables
string
variables
array
variables
#references
Each entry in each of the four lists has an accompanying
top pointer for its associated list of line numbers. The mark
CCH is used to mark the end of each line number list. A typi¬
cal variable item looks like this:
variable — stored LO/HI — for
example the variable A1 would be
stored 3141H
link to next variable in this list in
alphabetic order - stored in typi¬
cal LO/HI address format - will
be BBH for last item
ignored — 2 bytes
top pointer to list of line numbers
associated with this particular
variable
The list of line numbers associated with each variable in
each list is constructed in a similar, but simpler, fashion:
line number in which variable was
referenced — stored LO/HI
link to next line number in this
list - stored LO/HI — will be
CCH for last item in the list
Pacie 26
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
151
The entire program is read from the disk, one 256 byte
block at a time, and scanned for the purpose of constructing
these lists. When this is completed, the lists are followed in
order from beginning to end and the stored variables and line
numbers are formated and printed to produce the cross-
reference lists. Each list is printed with its own header, i.e.
STRING VARIABLES. And the entry NULL LIST is printed
for any list that is empty.
The diagram below represents the multi-list structure in
somewhat stylized fashion:
SYTOP STTOP ARTOP NMTOP
The variables which were found in the program are stored
in ASCII in the appropriate list so their conversion for printing
is straightforward. The line numbers that are placed in the
lists, however, are stored as two byte LO/HI binary values.
The algorithm used to convert these to ASCII for printing is
fairly simple, if somewhat bulky. Taking the binary value as
an ordered 16 bit field, the program uses a 5 byte work area
to construct the resulting decimal number. A table is provided
(BASE:) which represents, as 5 single digits, the decimal num¬
ber associated with each bit position of the 16 bit binary
value. If a bit in the binary value is “on,” then the five digits
associated with that bit position are added to the five byte
work area along with any necessary “carry’s” from byte to
byte. If, on the other hand, a bit in the binary value is “off,”
then the pointer into the table (BASE:) is bumped down 5 to
point to the next series of 5 values. When this process is
complete, 30H is added to each byte of the 5 byte work area
to yield the desired ASCII value.
This program has proven useful in its own right. But it is
worth mentioning that a modification of this same idea,
directed solely at line number references, would be the basis
for a program which would “compact” BASIC programs by
removing unnecessary line numbers. Similarly, this sort of
cross-reference compilation would form the basis of “pass
one” of more sophisticated software such as a compiler.
A compiler! Now there’s an idea.
Listing
0005
;
THIS PROGRAM PROVIDES SOFTWARE SUPPORT FOR
0010
;
PROGRAMS WRITTEN IN NORTHSTAR BASIC. IT COMPILES
0015
;
AND PRINTS
FOUR LISTS* 1)A LIST OF VARIABLE NAMto
0020
;
USED AND LINES IN WHICH EACH OF THEM OCCURS* 2)h
002S
;
LIST OF STRING VARIABLE NAMES USED AND LINES IN
0030
j
WHICH EACH
OCCURS. 3)A LIST OF ARRAY VARIABLE
0035
;
NAMES AND LINES IN WHICH EACH OCCURS* AND 4) A
0040
;
LIST OF LINE NUMBERS REFERENCED IN GOTO AND GOSUo
0045
;
STATEMENTS
AND LINE NUMBERS IN WHICH THEY ARE
0050
;
REFERENCED
0055
;
2A00
0060
ORG
2A00H
2A00
214233
0065
LXI
H* STACK*49
2A03
F9
0070
SPHL
2010
0075
ClN s EQU
2010H
200C
0080
COUTt EQU
200DH
20 1C
0085
DIRCK* EQU
20 1CH
2022
0090
RDCSKi EQU
2022H
2028
0095
EXITi EQU
2028H
0100
i
0105
;
PRINT HEADER
0 1 10
;
2A04
0E1F
0115
START* MV1
C* 31
2A06
218730
0120
LXI
H* HDR 1
2A09
CD5E30
0125
CALL
PRINT
2A0C
CD6830
0 130
CALL
CRLF
0 135
;
0 140
;
PRINT FILE
NAME PROMPT
0045
;
2A0F
0EI 1
0150
ASKFLs MVI
C* 17
2A11
21A630
0155
LXI
H*HDR2
2A14
CD5E30
0 160
CALL
PRINT
2A17
0E0A
0165
MVI
C* 10
2A19
218731
0170
LXI
H* PNAME
0175
0180
;
BLANK PROGRAM NAME AREA
0 185
;
2A1C
3620
0190
BLNAM* MVI
M* 20H
2A1E
23
0195
I NX
H
2A1F
0D
0200
DCR
C
2A20
C21C2A
0205
JNZ
BLNAM
2A23
0E09
0210
MVI
C* 9
2A25
218731
0215
LXI
H* PNAME
0220
;
0225
;
ACCEPTS FILE NAME. USES REG C AS COUNTER AND
0230
;
ACCEPTS UP
TO 8 CHARACTERS. TAKES CARE OF
0235
;
BLANKING CHAR IN RESPONSE TO BACKSPACE <5FH).
0240
;
ROUTINE TERMINATES WHEN CR <0DH) IS ENCOUNTERED.
0245
;
2A28
CD1020
0250
1NF1L * CALL
CIN
2A2B
32B232
0255
STA
HOLDT
2A2E
FE0D
0260
CPI
0DH
2A30
CA6F2A
0265
JZ
INUNT
2A33
FE5F
0270
CPI
5FH
2A35
C2542A
0275
JNZ
STORE
2A38
3E09
0280
MVI
A* 9
2A3A
B9
0285
CMP
C
2A3B
CA282A
0290
JZ
INFIL
2A3E
3AB232
0295
LDA
HOLDT
2A41
2B
0300
DCX
H
2A42
0C
0305
INR
C
2A43
47
0310
MOV
B* A
2A44
CD0D20
0315
CALL
COUT
2A47
0620
0320
MVI
B* 20H
2A49
CD0D20
0325
CALL
COUT
2A4C
065F
0330
MVI
B* 5FH
2A4E
CD0D20
0335
CALL
COUT
2A51
C3282A
0340
JMP
INFIL
0345
;
0350
1
PLACES CHARACTERS FROM INFIL* SEQUENTIALLY
0355
;
INTO AREA CALLED 'PNAME' TO BUILD INPUT
0360
;
FILE NAME.
PRINTS'’NAME'TOO LONG* ERROR
0365
;
IF 8 CHARACTERS ARE EXCEEDED.
0370
;
2A54
77
0375
STORE* MOV
M* A
2A55
47
0380
MOV
B* A
2A56
CD0D20
0365
CALL
COUT
2A59
23
0390
1NX
H
2A5A
0D
0395
DCR
C
2A5B
C2282A
0400
JNZ
INFIL
2A5E
CD6830
0405
CALL
CRLF
2A6 1
0E10
0410
MVI
C* 16
2A63
211031
0415
LXI
H*HDR7
2A66
CD5E30
0420
CALL
PRINT
2A69
CD6830
0425
CALL
CRLF
2A6C
C30F2A
0430
JMP
ASKFL
0435
;
0440
;
ACCEPTS DISK UNIT NUMBER. CHECKS TO MAKE
0445
;
SURE INPUT
IS ASCII 1* 2* OR 3.
0450
;
2A6F
0E0C
0455
INUNT* MVI
C* 12
2A7 1
21B730
0460
LXI
H*HDR3
2A7 4
CD6830
0465
CALL
CRLF
2A77
CD5E30
0470
CALL
PRINT
2A7A
219131
0475
LXI
H*DRIVE
2A7D
CD1020
0480
CALL
CIN
2A80
47
0485
MOV
B* A
2A8 1
CD0D20
0490
CALL
COUT
2A84
FE31
0495
CPI
31H
2A86
CAA42A
0500
JZ
GETCR
2A89
FE32
0505
CPI
32H
2A8B
CAA42A
0510
JZ
GETCR
2A8E
FE33
0515
CPI
33H
2A90
CAA42A
0520
JZ
GETCR
0525
;
Number 44
152
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 27
0530
;
PRINTS ’INVALID UNIT’ ERROR IF INPUT fl
U 2B40 AF
1085
NEVLN: XRA
A
0535
;
IS NOT EQUAL TO ASCII 1j 2, OR 3. (
J 2B41 329732
1090
STA
MARK
0540
;
r
) 2B44 3C
1095
INR
A
2A9 3
CD6830
0545
ERUNTs CALL
CRLF J
) 2B45 EB
1100
XCHG
2A96
0E0C
0550
MVI
C, 12 (
) 2B46 BE
1 105
CMP
M
2A96
212031
0555
LX I
H.HDR8 (
1 2B47 CABC2D
1 1 10
JZ
FRTRN
2A9B
CD5E30
0560
CALL
PRINT j
j 2B4A EB
1115
XCHG
2A9E
CD6830
0565
CALL
CRLF j
) 2B4B CD7330
1 120
CALL
NXTCR
2AA1
C36F2A
0570
JMP
INUNT )
J 2B4E 1A
1 125
LDAX
D
0575
J 2B4F 32A232
1130
STA
LOLIN
0580
TRIMS ASCII INPUT UNIT # TO BINARY VALUE (
j 2B52 CD7330
1135
CALL
NXTCR
0585
AND STORES
IT IN AREA CALLED ’DRIVE’. ACCEPTS ft
J 2B55 1A
1 140
LDAX
D
0590
CR TO CONTINUE. ANY OTHER INPOT CAUSES ft
J 2B56 32A332
1 145
STA
HIL1N
0595
’INVALID UNIT’ ERROR. PUTS ADDRESS OF PROGRAM (
) 2B59 AF
1150
XRA
A
0600
NAME IN REG H7L AND VALUE OF DRIVE t IN REG ft
) 2B5A 32A132
1 155
STA
LNTAB
0605
A. CALLS DOS DIRECTORY LOOKUP ROUTINE )
) 2B5D CD7330
1160
CALL
NXTCR
0610
AT 201CH.
IF CARRY BIT IS SET ON RETURN ft
j 2B60 62
1165
NEVL1: MOV
H. D
0615
•NO PROGRAM’ ERROR IS PRINTED. ft
\ 2B61 6B
1170
MOV
Lj E
0620
}
) 2B62 3E20
1175
MVI
Aj 20H
2AA4
E60F
0625
GETCRt AN1
0FH )
j 2B64 BE
1 180
CMP
M
2AA6
77
0630
MOV
Mj A )
\ 2B65 CAB62B
1 185
JZ
NEVL6
2AA7
CD 1020
0635
CALL
CIN )
( 2B68 3E8F
1 190
MVI
Aj 8FH
2AAA
47
0640
MOV
Bj A /
j 2B6A BE
1 195
CMP
M
2AAB
CD0D20
0645
CALL
COUT (
) 2B6B C2732B
1200
JNZ
NEVL2
2AAE
FE0D
0650
CPI
0DH )
j 2B6E 3E01
1205
MVI
Aj 1
2ABB
C2932A
0655
JNZ
ERUNT (
j 2B70 329732
1210
STA
MARK
2AB3
0 60A
0660
MVI
Bj 0 AH (
) 2B73 3E22
1215
NEVL2: MVI
Aj 22H
2AB5
CD0D20
0665
CALL
COUT
( 2B75 BE
1220
CMP
M
2AB8
3A9131
0670
LDA
DRIVE
( 2B76 C2902B
1225
JNZ
NEVL4
2ABB
218731
0675
LX I
HjPNAME
j 2B79 3A9732
1230
LDA
MARK
2ABE
37
0680
STC
|j
2B7C FE02
1235
CPI
02H
2ABF
3F
0685
CMC
j
2B7E C2882B
124e
JNZ
NEVL3
2AC0
CD1C20
0690
CALL
D1RCK (
2B81 AF
1245
XRA
A
2AC3
D2D42A
0695
JNC
CKTYP
2B82 329732
1250
STA
MARK
2 AC 6
0E19
0700
MVI
Cj 25 <i
2B85 C3B62B
1255
JMP
NEVL6
2AC8
21C330
0705
LX I
H.HDR4
2B86 3E02
1260
NEVL3: MVI
Aj 2
2ACB
CD5E30
0710
CALL
PRINT
2B8A 329732
1265
STA
MARK
2ACE
CD6830
0715
CALL
CRLF <1
2B8D C3B62B
1270
JMP
NEVL6
2AD1
C30F2A
0720
JMP
ASKFL
2B90 3A9732
1275
NEVL4: LDA
MARK
0725
;
|
2B93 FE00
1280
CPI
0H
0730
;
CHECKS FILE TYPE TO INSURE IT IS TYPE 2. ft
2B95 C2B62B
1285
JNZ
NEVL6
0735
;
||
2B98 3E9A
1290
MVI
Aj 9AH
2AD4
3600
0740
CKTYPl MVI
B, 0
2B9A BE
1295
CMP
M
2AD6
2 E04
0745
MVI
Cj 4
2B9B C2A42B
1300
JNZ
NEVL5
2AD8
09
0750
DAD
B
2B9E CDC82B
1305
CALL
STNUM
2AD9
3E02
0755
MVI
A. 2
2BA1 C3B62B
1310
JMP
NEVL6
2ADB
BE
0760
CMP
M
2BA4 3E40
1215
NEVL5: MVI
Aj 40H
2ADC
CAED2A
0765
JZ
STADD
2BA6 BE
1320
CMP
M
2ADF
I3E1 2
0770
MVI
Cj 18
2BA7 D2B62B
1325
JNC
NEVL6
2AE1
21DC30
0775
LX I
HjHDRS
2BAA 3E5A
1330
MVI
Aj 5 AH
2AE4
CD5E30
0780
CALL
PRINT
2BAC BE
1335
CMP
M
2AE7
CD6830
0785
CALL
CRLF
2BAD DAB62B
1340
JC
NLWL6
2AEA
C30F2A
0790
JMP
ASKFL
2BB0 CDEA2E
1345
CALL
GETSY
0795
I
2BB3 C3B92B
1350
JMP
NEVL7
0800
l
STORES DATA FROM DISK DIRECTORY FOR THE FILE
2BB6 CD7330
1355
NEVL6: CALL
NXTCR
0805
l
IN AREA CALLED ’DIR*. |
2BB9 3E0D
1360
NEVL7: MVI
Aj0DH
08 10
l
2BBB 21A 132
1365
LXI
HjLNTAB
2 AEL
2B
08 15
STADDi DCX
H (
2BBE BE
1370
CMP
M
2AEE
2B
0820
DCX
H (
2BBF C2602B
1375
JNZ
NEVL1
2AEF
2B
0825
DCX
H (
2BC2 CD7330
1380
CALL
NXTCR
2AF0
2B
0830
DCX
H (
2BC5 C3402B
1385
JMP
NEVLN
2AF 1
OE08
0835
MVI
Cj 8
1390
;
2AF 3
110933
0840
LXI
D. DIR (
139 5
; EXTRACTS A
LINE NUMBER
REFERENCE
2AF 6
7E
0845
STADli MOV
AjM |
J
1400
; AND PLACES
IT IN ’VALHI
’ AND ’VALLO
^F7
.2
0850
STAX
D
A
1405
i THEN CALLS
THE SEARCH AND INSERT
2AF8
23
0855
INX
H
A
1410
i NODE ROUTINES
2AF9
13
0860
I NX
D
A
1415
;
2AFA
(ID
0865
DCP.
C
A 2BC8 CD7330
1420
STNUM : CALL
NXTCR
2AFB
C2F62A
0870
JNZ
STAD1
A 2BCB 1A
1425
LDAX
D
0875
J
A 2BCC 32A532
1430
STA
VALLO
0880
;
SETS LINKS
IN AREA CALLED ’TABLE’. INITIALIZES
A 2BCF CD7330
1435
CALL
NXTCR
0885
;
THE TOP POINTERS FOR THE FOUR LISTS ’SYTOP’j
A 2BD2 1A
1440
LDAX
D
0890
;
* STTOP * j ’
ARTOP * * AND ’ NMTOP ’ . IN1TIALIZES " THE
A 2BD3 32A432
1445
STA
VALHI
0895
;
Availability pointer ’Avail*.
\ 2BD6 AF
1450
XRA
A
0900
;
>
\ 2BD7 32A132
1455
STA
LNTAB
2AFE
2600
0905
MVI
Hj 0 >
\ 2BDA 2AAC32
1460
LHLD
NMTOP
2B00
2E00
0910
MVl
Lj 0 )
< 2BDD 22B032
1465
SHLD
TOP
2B02
224333
09 15
SHLD
ADDR )
< 2BE0 CD7A2C
1470
CALL
SERCH
2B05
0600
0920
MVI
Bj 0 )
{ 2BE3 2AB032
1475
LHLD
TOP
2B07
0E04
0925
MVI
C j 4 >
< 2BE6 22AC32
1480
SHLD
NMTOP
2B09
1 18F33
0930
LXI
Dj TABLE*2 )
< 2BE9 C9
148 5
RET
2B0C
2A4333
0935
SLINK: LHLD
ADDR )
*
1490
;
2B0F
23
0940
INX
H )
\
1495
; EXTRACT A SYMBOL AND DETERMINE VHIC1
2B10
3E0C
0945
MVI
A* 0CH
1500
; LIST IT BELONGS IN. CALLS THE
2B12
DC
0950
CMP
H
1505
J SEARCH AND
INSERT NODE
ROUTINES.
2B13
CA232B
0955
JZ
STOPS
1510
;
2B16
224333
0960
SHLD
ADDR
< 2BEA 3E20
1515
GETSY: MVI
Aj 20H
2B 19
62
0965
MOV
HjD
< 2BEC 32A532
1520
STA
VALLO
2B1A
6B
0970
MOV
Lj e
< 2BEF 32A432
1525
STA
VALHI
2B1B
09
0975
DAD
B
< 2BF2 1A
1530
LDAX
D
2B1C
EB
0980
XCHG
< 2BF3 32A432
1535
STA
VALHI
2B1D
73
0985
MOV
Mj E
( 2BF6 CD7330
1540
CALL
NXTCR
2B1E
23
0990
INX
H
( 2BF9 3E0D
1545
MVI
Aj0DH
2B1F
72
0995
MOV
MiD }
/ 2BFB 21A132
1550
LXI
HjLNTAB
2B20
C30C2B
1000
JMP
SLINK \
j 2BFE BE
1555
CMP
M
2B23
3EFF
1005
STOPS: MVI
Aj0FFH V
j 2BFF C2082C
1560
JNZ
GETS 1
2B25
23
1010
INX
H V
j 2C02 CD4A2C
1565
CALL
STRSY
2B26
77
1015
MOV
Mj A V
j 2C05 C3492C
1570
JMP
GETS5
2B27
2 6BB
1020
MVI
Hj 0BBH V
( 2C08 62
1575
GETS 1 : MOV
HjD
2B29
2 EBB
1025
MVI
Lj 0BBH V
( 2C09 6B
1580
MOV
LjE
2B2B
22A632
1030
SHLD
SYTOP V
( 2C0A 3E2F
158 5
MVI
Aj 2FH
2B2E
22A832
1035
SHLD
STTOP V
( 2C0C BE
1590
CMP
M
2B31
22AA32
1040
SHLD
ARTOP V
( 2C0D D22C2C
1595
JNC
GETS2
2B34
22AC32
1045
SHLD
NMTOP \
j 2C10 3E39
1600
MVI
Aj 39H
2B37
218F33
1050
LXI
HiTABLE+2 V
( 2C12 BE
1605
CMP
M
2B3A
22AE32
1055
SHLD
AVAIL V
( 2C13 DA2C2C
1610
JC
GETS2
2B3D
CD2F30
1060
CALL
RDBLK V
{ 2C16 1A
1615
LDAX
D
1065
;
y
j 2C17 32A532
1620
STA
VALLO
1070
;
BEGINS PROCESSING FOR A LINE OF BASIC CODE.
( 2C1A CD7330
1625
CALL
NXTCR
1075
;
STORES LINE NUMBER AND LINE LENGTH.
( 2C1D 3E0D
1630
MVI
Aj 0DH
1030
;
>
{ 2C1F 21A132
1635
LXI
HjLNTAB
y
j 2C22 BE
1640
CMP
M
>
( 2C23 C22C2C
1645
JNZ
GETS2
Page 28
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
153
2C26 CD4A2C
2C29 C3492C
2C2C 62
2C2D 6E
2C2E 3E24
2C30 BE
2C31 C23A2C
2C34 CD5A2C
2C37 C3492C
2C3A 3EE0
2C3C BE
2C3D C2462C
2C40 CD6A2C
2C43 C3492C
2C46 CD4A2C
2C49 C9
2C4A 2AA632
2C4D 22B032
2C50 CD7A2C
2C53 2AB032
2C56 22A632
2C59 C9
2C5A 2AA832
2C5D 22B032
2C60 CD7A2C
2C63 2AB032
2C66 22A832
2C69 C9
2C6A 2AAA32
2C6D 22B032
2C70 CD7A2C
2C7 3 2AB032
2C76 22AA32
2C79 C9
2C7A 229C32
2C7D EB
2C7E 229E32
2C81 3EBB
2C83 329832
2C86 329932
2C89 2AAE32
2C8C 229A32
2C8F 2B
2C90 3AA432
2C93 77
2C94 2B
2C95 3AA532
2C98 77
2C99 23
2C9A 23
2C9B 3EBB
2C9D 77
2C9E 23
2C9F 77
2CAB 23
2CA1 23
2CA2 23
2CA3 7E
2CA4 32AE32
2CA7 3ECC
2CA9 77
2CAA 23
2CAB 7E
2CAC 32AF32
2CAF 3ECC
2CB1 77
2CB2 2A9C32
2CB5 3EBB
2CB7 BC
2CB8 C2C92C
2CBB BD
2CBC C2C92C
2CBF 2A9A32
2CC2 22B032
2CC5 CD752D
2CC8 C9
2CC9 2B
2CCA 56
2CCB 3AA432
2CCE BA
2CCF CA322D
2CD2 D2FB2C
2CD5 2A9A32
2CD8 3A9C32
2CDB 77
2CDC 23
2CD0 3A9D32
2CE0 77
SCSI 2A9832
2CE4 3EBB
2CE6 BC
2CE7 C2EE2C
2CEA BD
Number 44
154
1650
CALL
STRSY
J) 2CEB
CABF2C
2215
JZ
SERC1
1655
JMP
GETS5
J) 2CEE
3A9A32
2220 DGRTli
LDA
PRSNT
1660 GETS2I
MOV
Hi D 1
J) 2CF1
77
2225
MOV
Ms A
1665
MOV
Li E l
J) 2CF2
23
2230
I NX
H
1670
MVI
A.24H 1
}) 2CF3
3A9B32
2235
LDA
PRSNT* 1
1675
CMP
M 1
J) 2CF6
77
2240
MOV
Ms A
1680
JNZ
GETS3 l
J) 2CF7
CD752D
2245
CALL
LNNUM
1685
CALL
STRST 1
J) 2CFA
C9
2250
RET
1690 JMP GETS5
1695 GETS3: MVI As0E0H
1700 CMP M
1705 JNZ GETS4
1710 CALL STRAR
1715 JMP GETS5
1720 GETS4I CALL STRSY
1725 GETS5: RET
1730 ;
1735 J SETS SYMBOL LIST TOP POINTER AND CALLS
1740 ; SEARCH AND INSERT NODE ROUTINES.
1745 ;
1750 STRSYi
LHLD
SYTOP
1755
SHLD
TOP
1760
CALL
SERCH
1765
LHLD
TOP
1770
SHLD
SYTOP
1775
1780 ;
1785 I
1790 J
1795 ;
1800
1805
1810
18 15
1820
1825
1830
1835
18 40
1845
SETS TOP POINTER TO STRING LIST TOP AND
CALLS SEARCH AND INSERT NODE ROUTINES.
STRSTl LHLD
STTOP
SHLD
TOP
CALL
SERCH
LHLD
TOP
SHLD
STTOP
RET
SETS TOP POINTER TO ARRAY LIST TOP AND
CALLS SEARCH AND INSERT NODE ROUTINES.
1850
STRAR» LHLD
ARTOP
1855
SHLD
TOP
1860
CALL
SERCH
1865
LHLD
TOP
1870
1875
1880
SHLD
RET
;
ARTOP
1885
1890
; SEARCH AND
;
STORE 1
1895
1900
SERCHi SHLD
XCHG
NEXT
1905
SHLD
POINT
19 10
MVI
As0BBH
1915
STA
LAST*
1920
STA
LAST*1
1925
LHLD
AVAIL
1930
SHLD
PRSNT
1935
DCX
H
1940
LDA
VALHI
1945
MOV
Ms A
1950
DCX
H
1955
LDA
VALLO
1960
MOV
Ms A
1965
I NX
H
19.70
I NX
H
1975
MVI
As 0BBH
1980
MOV
Ms A
1985
INX
H
1990
MOV
Ms A
1995
INX
H
2000
INX
H
2005
INX
H
2010
MOV
AsM
2015
STA
AVAIL
2020
MVI
As 0CCH
2025
MOV
Ms A
2030
INX
H
2035
MOV
AsM
2040
STA
AVAIL*
2045
MVI
As 0CCH
2050
MOV
Ms A
2055
LHLD
NEXT
2060
MVI
As 0BBH
2065
CMP
H
2070
JNZ
SERC2
2075
CMP
L
2080
JNZ
SERC2
2085
SERCH LHLD
PRSNT
2090
SHLD
TOP
2095
2100
CALL
RET
LNNUM
2105
SERC21 DCX
H
21 10
MOV
DsM
2115
LDA
VALHI
2120
CMP
D
2125
JZ
DEQUA
2130
2135
JNC
DLESA
2140
; SETS THE LINKS IN
2145
; TO REFLECT
THE PRl
2150
2155
i CURRENT ITEM.
;
2160
DGRTAi LHLD
PRSNT
2165
LDA
NEXT
2170
MOV
Ms A
2175
INX
H
2180
LDA
NEXT*1
2185
MOV
Ms A
2190
LHLD
LAST
2195
MVI
As 0BBH
2200
CMP
H
2205
JNZ
DGRT1
2210
CMP
L
2D75
2D78
2D79
2D7 A
2D7B
2D7C
2D7E
2D7F
2D82
2D8 3
2D84
2D87
2D88
2D8B
2 DSC
2D8D
2D90
2D9 1
2D94
2D95
2D96
2D99
2D9A
2D9B
2A9A32
23
23
23
23
3ECC
BE
C2B52D
23
BE
C2B42D
2B
3AAE32
77
23
3AAF32
77
2AAE32
2B
2B
3AA232
77
23
3AA332
2255
2260
2265
2270
2275
CONTINUES TO SEARCH THE APPROPRIATE
LIST FOR THE PROPER PLACE IN WHICH
TO INSERT THE CURRENT ITEM.
2CFB
3 EBB
2280
DLESA«
MVI
As 0BBH
2CFD
2A9C32
2265
LHLD
NEXT
2D00
BC
2290
CMP
H
2D0 1
C2182D
2295
JNZ
DLES2
2D04
BD
2300
CMP
L
2D05
C2162D
2305
JNZ
DLES2
2D08
2A9832
2310
DLES1l
LHLD
LAST
2D0B
3A9A32
2315
LDA
PRSNT
2D0E
77
2320
MOV
Ms A
2D0F
23
2325
INX
H
2D 1 0
3A9B32
2330
LDA
PRSNT* 1
2D 1 3
77
2335
MOV
Ms A
2D 14
CD752D
2240
CALL
LNNUM
2D 1 7
C9
2345
RET
2D 16
2A9C32
2350
DLES2 l
LHLD
NEXT
2D 1B
229832
2355
SHLD
LAST
2D 1E
5E
2360
MOV
EsM
2D1F
23
2365
INX
H
2D20
56
2370
MOV
DsM
2D2 1
EB
2375
XCHG
2D22
229C32
2380
SHLD
NEXT
2D25
3 EBB
2385
MVI
As 0BBH
2D27
BC
2390
CMP
H
2D28
C2C92C
2395
JNZ
SERC2
2D2B
BD
2400
CMP
L
2D2C
C2C92C
2405
JNZ
SERC2
2D2F
C3062D
2410
JMP
DLES1
2415
;
2420
; CHECKS TO
SEE IF T1
2425
i IS ALREADY
IN THE i
2430
;
2D32
2B
2435
DEQUA:
DCX
H
2D33
56
2440
MOV
DsM
2D34
3AA532
2445
LDA
VALLO
2D37
BE
2450
CMP
M
2D38
CA412D
2455
JZ
DEQU1
2D3B
D2FB2C
2460
JNC
DLESA
2D3E
C3D52C
2465
JMP
DGRTA
2D41
2AAE32
2470
DEQU1:
LHLD
AVAIL
2D44
2B
2475
DCX
H
2D45
2B
2460
DCX
H
2D46
2B
2485
DCX
H
2D47
3AAF32
2490
LDA
AVAIL*]
2D4A
77
2495
MOV
Ms A
2D4B
2B
2500
DCX
H
2D4C
3AAE32
2505
LDA
AVAIL
2D4F
77
2510
MOV
Ms A
2D50
2B
2515
DCX
H
2D51
2B
2520
DCX
H
2D52
2B
2525
DCX
H
2D53
EB
2530
XCHG
2D54
2AAE32
2535
LHLD
AVAIL
2D57
2B
2540
DCX
H
2D58
2B
2545
DCX
H
2D59
2B
2550
DCX
H
2D5A
2B
2555
DCX
H
2D5B
22AE32
2560
SHLD
AVAIL
2D5E
EB
256 5
XCHG
2D5F
3AAF32
2570
LDA
AVAIL*1
2D62
77
2575
MOV
Ms A
2D63
2B
2580
DCX
H
2D64
3AAE32
2585
LDA
AVAIL
2D67
77
2590
MOV
Ms A
2D68
22AE32
2595
SHLD
AVAIL
2D6B
2A9C32
2600
LHLD
NEXT
2D6E
229A32
2605
SHLD
PRSNT
2D7 1
CD752D
2610
CALL
LNNUM
2D7 4
C9
2615
RET
2620
;
2625
2630
2635
2640
2645
2650
2655
266e
2665
2670
2675
2680
2685
2690
2695
2700
2705
2710
2715
2720
2725
27 30
2735
274e
2745
2750
2755
2760
2765
2770
2775
INSERTS THE LINE NUMBER FOR THE
CURRENT ITEM IN THE LINE NUMBER
LIST FOR THAT ITEM. THE NEW
LINE NUMBER IS ADDED AT THE END
OF THE LIST SINCE THEY ARE ENCOUNTERED
IN ORDER.
LHLD
PRSNT
INX
H
INX
H
INX
H
INX
H
MVI
As 0CCH
CMP
M
JNZ
LNNU3
INX
H
CMP
M
JNZ
LNNU2
DCX
H
LDA
AVAIL
MOV
Ms A
INX
H
LDA
AVAIL*
MOV
Ms A
LHLD
AVAIL
DCX
H
DCX
H
LDA
LOLIN
MOV
Ms A
INX
H
LDA
HILIN
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 29
2D9S
77
2780
MOV
Ms A
2D9 7
23
2785
INX
H
2 DAO
7E
2790
MOV
AsM
2DA1
32AE32
2795
STA
AVAIL
2DA4
3ECC
2800
MVI
As 0CCH
2 DA 6
77
2805
MOV
Ms A
2DA7
23
2810
INX
H
2 DAG
7E
2815
MOV
AsM
2DA9
32AF32
2820
STA
AVAIL* 1
2DAC
3ECC
2825
MVI
As 0CCH
2 DAE
77
2830
MOV
Ms A
2DAF
2A9E32
28 35
LHLD
POINT
2DB2
EB
2840
XCHG
2DB3
C9
2845
RET
2DB<i
2B
28 50
LNNU21
DCX
H
2DB5
5E
2855
LNNU3l
MOV
EsM
2DB6
23
2860
INX
H
2DB7
56
2865
MOV
DsM
2 DBG
EB
2870
XCHG
2DB9
C37C2D
2875
JMP
LNNU1
2880
;
2885 ; PRINTS THE NECESSARY HEADERS AND
2890 ; LOADS THE APPROPRIATE LIST TOP POINTERS
2895 ; FOR USE BY THE SEARCH AND PRINT ROUTINES.
2900 ;
2 DBG
0E12
2905
PRTRNl MVI
Cs 18
2 DBF.
214131
29 10
LXl
HsHDRl1
2DCI
CD6830
2915
CALL
CRLF
2DC4
CD5E30
2920
CALL
PRINT
2DCT
CD6830
2925
CALL
CRLF
2 DC A
2AA632
2930
LHLD
SYTOP
2DCD
22B032
2935
SHLD
TOP
2DDC
3E0 1
2940
MVI
As 1
2DD2
329732
2945
STA
MARK
2DD5
CD2F2E
2950
CALL
FNDSY
2DD8
CD6830
2955
CALL
CRLF
2 DDE
0E10
2960
MVI
Cs 16
2DDD
215331
2965
LXI
HsHDR12
2DE0
CD5E30
2970
CALL
PRINT
2DE3
CD68 30
2975
CALL
CRLF
2DE6
2AA832
2980
LHLD
STTOP
2DE9
22B032
2985
SHLD
TOP
2DEC
3E02
2990
MVI
As 2
2DEE
329732
2995
STA
MARK
2DF 1
CD2F2E
3000
CALL
FNDSY
2DF4
CD6830
3005
CALL
CRLF
2DF7
0E0F
3010
MVI
Cs 15
2DF9
216331
3015
LXI
Hs HDR13
2DFC
CD5E30
3020
CALL
PRINT
2DFF
CD6830
3025
CALL
CRLF
2E02
2AAA32
3030
LHLD
ARTOP
2E05
22B032
3035
SHLD
TOP
2E08
3E03
3040
MVI
As 3
2E0A
329732
3045
STA
MARK
2E0D
CD2F2E
3050
CALL
FNDSY
2E10
CD6630
3055
CALL
CRLF
2E13
0E0C
3060
MVI
Cs 12
2E15
217231
3065
LXI
Hs HDR 1 4
2E18
CD5E30
3070
CALL
PRINT
2E1B
CD6830
3075
CALL
CRLF
2E1E
2AAC32
3080
LHLD
NMTOP
2E2 1
22B032
3085
SHLD
TOP
2E24
3E04
3090
MVI
As 4
2E26
329732
3095
STA
MARK
2E29
CD2F2E
3000
CALL
FNDSY
2E2C
C32820
3105
JMP
EXIT
3110 ;
3115 J THIS SECTION USES THE CENTENTS OF 'TOP*
3120 ; AND FOLLOWS THE LINKS FOR THE APPROPRIATE
3125 ; LIST. AT EACH ELEMENT IT LOADS ’HOLDT'
3130 ; WITH THE LINE FOR THE LINE NUMBER
3135 ; REFERENCES AND FOLLOWS THAT LI ST* PRINTING
3140 i THE NUMBERS AS IT GOES.
3145 ;
2E2F 2AB032 3150 FNDSY* LHLD TOP
2E32 3EBB 3155 MVI A* 0BBH
2E34 BC 3160 CMP H
2E35 C24B2E 3165 JNZ FNDS1
2E38 BD 3170 CMP L
2E39 C24B2E 3175 JNZ FNDS1
2E3C 0E09 3180 MVI Cs9
2E3E 217E31 3185 LXI HsHDRl5
2E41 CD6830 3190 CALL CRLF
2E44 CD5E30 3195 CALL PRINT
2E47 CD6830 3200 CALL CRLF
2E4A C9 3205 RET
2E4B CD2130 3210 FNDSll CALL BLKLN
2E4E 2AB032 3215 LHLD TOP
2E51 5E 3220 MOV Es M
2E52 23 3225 INX H
2E53 56 3230 MOV DsM
2E54 2B 3235 DCX H
2E55 EB 3240 XCHG
2E56 229C32 3245 SHLD NEXT
2E59 3A9732 3250 LDA MARK
2E5C FE04 3255 CPI 4
2E5E
C28B2E
3260
JNZ
FNDS3
2E61
IB
3265
DCX
D
2E62
1A
3270
LDAX
D
2E63
32A432
3275
STA
VALHI
2E66
IB
3280
DCX
D
2E67
1A
3285
LDAX
D
2E68
32A532
3290
STA
VALLO
2E6B
CD842F
3295
CALL
CONVR
2E6E
214533
3300
LXI
HsPLINE
2E7 1
EB
3305
XCHG
2E72
21B432
3310
LXI
HsNUMBR
2E7 5
0E05
3315
MVI
Cs 5
2E77
7E
3320 FNDS21
MOV
AsM
2E78
12
3325
STAX
D
2E79
23
3330
INX
H
2E7A
13
3335
INX
D
2E7B
0D
3340
DCR
C
2E7C
C2772E
3345
JNZ
FNDS2
2E7F
2AB032
3350
LHLD
TOP
2E82
EB
3355
XCHG
2E8 3
IB
3360
DCX
D
2E84
IB
3365
DCX
D
2E85
CDDB2E
3370
CALL
LSTNM
2E88
C3C12E
3375
JMP
FNDS7
2E8B
214533
3380
FNDS31
LXI
HsPLINE
2E8E
IB
3385
DCX
D
2E8F
1A
3390
LDAX
D
2E90
77
3395
MOV
Ms A
2E9 1
23
3400
INX
H
2E92
IB
3405
DCX
D
2E9 3
1A
3410
LDAX
D
2E94
FE20
3415
CPI
20H
2E96
CA9B2E
3420
JZ
FNDS4
2E99
77
3425
MOV
Ms A
2E9A
23
3430
INX
H
2E9B
3A9732
3435
FNDS4i
LDA
MARK
2E9E
FE02
3440
CPI
2
2EA0
C2AC2E
3445
JNZ
FNDS5
2EA3
3E24
3450
MVI
As 2 AH
2EA5
77
3455
MOV
Ms A
2EA6
CDDB2E
3460
CALL
LSTNM
2EA9
C3C12E
3465
JMP
FNDS7
2EAC
FE03
3470
FNDS5*
CPI
3
2EAE
C2BE2E
3475
JNZ
FNDS6
2EB1
3E2S
348 0
MVI
As 28H
2EB3
77
3485
MOV
Ms A
2EB4
23
3490
INX
H
2EB5
3E29
3495
MVI
As 29H
2EB7
77
3500
MOV
Ms A
2EB8
CDDB2E
3505
CALL
LSTNM
2 EBB
C3C12E
3510
JMP
FNDS7
2EBE
CDDB2E
3515
FNDS6I
CALL
LSTNM
2EC 1
2A9C32
3520
FNDS7i
LHLD
NEXT
2EC4
3EBB
3525
MVI
As 0BBH
2EC6
BC
3530
CMP
H
2EC7
C2CF2E
3535
JNZ
FNDS8
2ECA
BD
3540
CMP
L
2ECB
C2CF2E
3545
JNZ
FNDS8
2ECE
C9
3550
RET
2ECF
CD6830
3555
FNDS8 l
CALL
CRLF
2ED2
2A9C32
3560
LHLD
NEXT
2ED5
22B032
3565
SHLD
TOP
2ED8
C34B2E
3570
JMP
FNDS1
3575 ;
3580 ; FOLLOWS EACH LINE NUMBER LIST AND PRINTS
3585 J THE FORMATED NUMBERS.
3590 i
2EDB 13 3595 LSTNMi INX D
2EDC 13 3600 INX D
2EDD 13 3605 INX D
2EDE 13 3600 INX D
2EDF 13 3615 INX D
2EE0 13 3620 INX D
2EE1 13 3625 INX D
2EE2 13 3630 INX D
2EE3 13 3635 INX D
2EE4 13 3640 INX D
2EE5 AF 3645 LSTNU XRA A
2EE6 329432 3650 STA TAB
2EE9 3E08 3655 MVI As 8
2EEB 329232 3660 STA LINCT
2EEE 3E0C 3665 MVI As 12
2EF0 329332 3670 STA CHRCT
2EF3 215133 3675 LXI HsPLINE*12
2EF6 22B232 3680 SHLD HOLDT
2EF9 IB 3690 LSTN21 DCX D
2EFA 1A 3695 LDAX D
2EFB 32A432 3700 STA VALHI
2EFE IB 3705 DCX D
2EFF 1A 3710 LDAX D
2F00 32A532 3715 STA VALLO
2F03 13 3720 INX D
2F04 13 3725 INX D
2F05 1A 3730 LDAX D
2F06 329832 3735 STA LAST
2F09 13 3740 INX D
2F0A 1A 3745 LDAX D
2F0B 329932 3750 STA LAST*1
2F0E CD842F 3755 CALL CONVR
2F11 2AB232 3760 LHLD HOLDT
2F14 EB 3765 XCHG
2F15 21B432 3770 LXI HsNUMBR
2F18 0E05 3775 MVI Cs5
2F1A 7E 3730 LSTN3* MOV AsM
2F1B 12 3785 STAX D
2F1C 23 3790 INX H
2F1D 13 3795 INX D
2F1E 0D 3800 DCR C
2F1F C21A2F 3805 JNZ LSTN3
2F22 13 3810 INX D
2F23 13 3815 INX D
2F24 EB 3820 XCHG
2F25 22B232 3825 SHLD HOLDT
2F28 219332 3830 LXI HsCHRCT
2F2B 3E07 3835 MVI As 7
2F2D 86 3840 ADD M
2F2E 329332 3845 STA CHRCT
2F31 3A9232 3850 LDA LINCT
2F34 3D 3855 DCR A
2F35 CA4E2F 3860 JZ LSTN4
2F38 329232 3865 STA LINCT
2F3B 2A9832 3870 LHLD LAST
2F3E EB 3875 XCHG
2F3F 3ECC 3880 MVI As0CCH
2F41 BA 3885 CMP D
2F42 C2F92E 3890 JNZ LSTN2
2F45 BB 3895 CMP E
2F46 C2F92E 3900 JNZ LSTN2
2F49 3E01 3905 MVI As 1
2F4B 329432 3910 STA TAB
Page 30
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
155
2F4E
3A9332
39 15
LSTN4:
LDA
CHRCT
2F5 1
4F
3920
MOV
C, A
2F52
214533
3925
LX I
H,PLINE
2F55
CD5E30
39 30
CALL
PRINT
2F58
CD6830
3935
CALL
CRLF
2F5B
3A9432
3940
LDA
TAB
2F5E
FE0 1
3945
CPI
1
2F60
C26A2F
3950
JNZ
LSTN6
2F63
2A9C32
3955
LSTN5:
LHLD
NEXT
2F66
22B032
3960
SHLD
TOP
2F69
C9
3965
RET
2F6A
2A9832
3970
LSTN6:
LHLD
LAST
2F6D
3ECC
3975
MV1
A, 0CCH
2F6F
BC
3880
CMP
H
2F70
C27A2F
3985
JNZ
LSTN7
2F73
BD
3990
CMP
L
2F7 4
C27A2F
3995
JNZ
LSTN7
2F77
C3632F
4000
JMP
LSTN5
2F7A
CD2130
4005
LSTN7:
CALL
BLKLN
2F7D
2A9832
4010
LHLD
LAST
2F80
EB
40 15
XCHG
2F8 1
C3E52E
4020
JMP
LSTN1
4025
;
4030 ; CONVERTS EACH NUMBER IN THE LINE NUMBER
4035 ; LISTS FROM HEX TO DECIMAL (ASCII). THIS IS
4040 ; DONE BY INSPECTING EACH BIT OF THE STORED
4045 ; LINE NUMBER BEGINNING WITH THE HIGH ORDER
4050 i BIT. IF THE BIT IS ON, THE APPROPRIATE VALUE
4055 ; (5 DIGITS) FROM THE DATA CALLED 'BASE:* ARE
4060 ; ADDED DECIMALLY, ONE DIGIT AT A TIME, TNTO
4065 i AN ACCUMULATOR AREA CALLED 'NUMBRi'.
4070
;
2F84
0E05
4075
CONVR:
MVI
C, 5
2F86
AF
4080
XRA
A
2F87
21B432
4085
LX I
H,NUMBR
2F8 A
77
4090
CONV1:
MOV
M, A
2F8B
23
4095
INX
H
2F8C
0D
4100
DCR
C
2F8D
C28A2F
4105
JNZ
CON VI
2F90
AF
41 10
XRA
A
2F9 1
329432
4115
STA
TAB
2F94
210833
4120
LX I
H,BASE-*79
2F97
EB
4125
XCHG
2F98
3AA432
4130
LDA
VALHI
2F9B
47
4135
C0NV2:
MOV
B, A
2F9C
0E08
4140
MVI
C, 8
2F9E
78
4145
C0NV3:
MOV
A, B
2F9F
E680
4 150
AN I
80H
2FA 1
C2AC2F
4155
JNZ
C0NV4
2FA4
IB
4160
DCX
D
2FA5
IB
4165
DCX
D
2FA6
IB
4170
DCX
D
2FA7
IB
4175
DCX
D
2FA8
IB
4180
DCX
D
2FA9
C3DD2F
4185
JMP
C0NV8
2FAC
2 IBS32
4190
C0NV4:
LX I
H,NUMBR*4
2FAF
AF
4195
XRA
A
2FB0
329532
4200
STA
CARRY
2FB3
3E05
4205
MVI
A, 5
2FB5
329632
4210
C0NV5:
STA
COUNT
2FB8
1A
4215
LDAX
D
2FB9
86
4220
ADD
M
2FBA
77
4225
MOV
M, A
2FBB
3A9532
4230
LDA
CARRY
2FBE
86
4235
ADD
M
2FBF
FE0A
4240
CPI
0 AH
2FC 1
CACC2F
4245
JZ
C0NV6
2FC4
D2CC2F
4250
JNC
C0NV6
2FC7
77
4255
MOV
M, A
2FC8
AF
4260
XRA
A
2FC9
C3D12F
4265
JMP
C0NV7
2FCC
D60A
4270
C0NV6:
SUI
0AH
2FCE
77
4275
MOV
M, A
2FCF
3E0 1
4280
MVI
A, 1
2FD1
329532
428 5
C0NV7:
STA
CARRY
2FD4
2B
4290
DCX
H
2FD5
IB
4295
DCX
D
2FD6
3A9632
4300
LDA
COUNT
2FD9
3D
4305
DCR
A
2FDA
C2B52F
4310
JNZ
C0NV5
2FDD
0D
4315
C0NV8:
DCR
C
2FDE
CAE72F
4320
JZ
C0NV9
2FE1
78
4325
MOV
A, B
2FE2
07
4330
RLC
2FE3
47
4335
MOV
B, A
2FE4
C39E2F
4340
JMP
C0NV3
2FE7
3A9432
4345
C0NV9:
LDA
TAB
2FEA
FE0 1
4350
CPI
1
2FEC
CAFA2F
4355
JZ
CON 10
2FEF
3E01
4360
MVI
A, 1
2FF1
329432
4365
STA
TAB
2FF4
3AA532
4370
LDA
VALLO
2FF7
C39B2F
4375
JMP
C0NV2
2FFA
0E05
4380
CON 10:
MVI
C, 5
2FFC
21B432
4385
LX I
H, NUMBR
2FFF
7E
4390
CON 1 1:
MOV
A, M
3000
C630
4395
ADI
30H
3002
77
4400
MOV
M, A
3003
3A9432
4405
LDA
TAB
3006
FE0 1
4410
CPI
1
3006
C21B30
4415
JNZ
CON 13
300B
3E30
4420
MVI
A, 30H
300D
BE
4425
CMP
M
300E
C21730
4430
JNZ
CON 12
3011
3E20
4435
MVI
A, 20H
3013
77
4440
MOV
M, A
3014
C31B30
4445
JMP
CON 13
3017
AF
4450
CON 12:
XRA
A
3018
329432
4455
STA
TAB
30 IB
23
4460
CON 13:
INX
H
30 1C
0D
4465
DCR
C
30 ID
C2FF2F
4470
JNZ
CONI 1
3020
C9
4475
RET
4480
4485
4490
; FILLS THE PRINT LINE WITH SPACES (20H).
3021
0E48
4495
BLKLN:
MVI
C, 72
3023
214533
4500
LX I
H,PLINE
3026
3E20
4405
MVI
A, 20H
3028
77
4510
BLKL1:
MOV
M, A
3029
23
4515
INX
H
302A
0D
4520
DCR
C
302B
C22830
4525
JNZ
BLKL1
302E
C9
4530
RET
4535
4540
4545
4550
4555
J THIS ROUTINE READS ONE 256 BYTE BLOCK
,* OF DATA FROM THE DISK INTO THE AREA
I CALLED 'DATA'.
302F
3E0 1
4560
RDBLK:
MVI
A, 1
3031
0601
4565
MVI
B, 1
3033
219131
4570
LX I
H,DRIVE
3036
4E
4575
MOV
C, M
3037
1 19231
4580
LX I
D,DATA
30 3A
2A0933
4585
LHLD
DIR
303D
23
4590
INX
H
303E
220933
4595
SHLD
DIR
3041
2B
4600
DCX
H
3042
CD2220
4605
CALL
RDDSK
3045
D25630
46 10
JNC
RDBL 1
3048
0E0E
4615
MVI
C, 14
304A
213331
4620
LX I
H,HDR10
304D
CD5E30
4625
CALL
PRINT
3050
CD6830
46 30
CALL
CRLF
3053
C32820
4635
JMP
EXIT
3056
AF
4640
RDBL1:
XRA
A
3057
32A032
4645
STA
BLKPT
305A
1 19231
4650
LX I
D,DATA
305D
C9
4655
RET
4660
;
4665
J PRINT STRING AT ADDRESS
4670
,* NUMBER OF
CHARACTERS IN
4675
;
305E
46
4680
PRINT:
MOV
B,M
305F
CD0D20
4685
CALL
COUT
3062
23
4690
INX
H
3063
0D
4695
DCR
C
3064
C25E30
4700
JNZ
PRINT
3067
C9
4705
RET
4710
;
4715
; INSERT CR
AND LF
4720
;
3068
060D
4725
CRLF:
MVI
B, 0DH
306A
CD0D20
4730
CALL
COUT
306D
060A
4735
MVI
B, 0 AH
306F
CD0D20
4740
CALL
COUT
3072
C9
4745
RET
4750
;
4755
; CHECK BLOCK ROUTINE
4760
;
3073
13
4765
NXTCR:
INX
D
3074
21A032
4770
LX I
H,BLKPT
3077
34
4775
INR
M
3078
CC2F30
4760
CZ
RDBLK
307B
62
4785
MOV
H, D
307 C
6B
4790
MOV
L, E
307 D
3E0D
4795
MVI
A, 0DH
307 F
BE
4800
CMP
M
3080
C28630
4805
JNZ
NXTC1
3083
32A132
48 10
STA
LNTAB
3086
C9
4815
NXTC1:
RET
48 20
t
4825
I HEADERS
3087
30A6
30B7
30C3
30DC
30EE
3110
3120
312C
3133
3141
3153
3163
3172
317E
3187
3191
3192
3292
329 3
3294
3295
3296
3297
3298
329A
329C
329E
32A0
32A1
32A2
32A3
32A4
32A5
32A6
32A8
32AA
3 2 AC
32AE
32B0
32B2
32B4
48 30
4E4F5254484835
4E414D45204840
4F4E2044524845
4E4F20505248 50
46494C452046 55
5441424C454860
4E414D45204865
494E56414C4870
4E4F20524F4875
415247554D4880
53594D424F4865
535452494E4890
41525241594895
4C494E45204900
4E554C4C204905
4910
49 15
4920
4925
4930
49 35
4940
4945
4950
4955
4960
4965
4970
4975
4980
4985
4990
4995
5000
5005
5010
5015
5020
5025
5030
5035
5040
DB
DB
DB
DB
DB
DB
DB
HDR1:
HDR2:
HDR3 i
HDR4:
HDR5:
HDR6:
HDR7 i
HDR8:
HDR9: DB
HDR10: DB
HDR11: DB
HDR12i DB
H DR131 DB
HDR14: DB
H DR 15« DB
PNAME: DS
DRIVE: DS
DATA: DS
LINCT: DS
CHRCT: DS
TAB: DS
CARRY: DS
COUNT: DS
MARK:
LAST:
PRSNT: DS
NEXT: DS
POINT: DS
BLKPT: DS
LNTAB: DS
LOLINi DS
HILIN: DS
VALHI: DS
VALLO: DS
SYTOP: DS
STTOP: DS
ARTOP: DS
NMTOP: DS
AVAIL: DS
TOP: DS
HOLDT: DS
NUMBR: DS
DS
DS
NORTHSTAR BASIC PROGRAM SUPPORT'
NAME OF PROGRAM: •
ON DRIVE #: '
NO PROGRAM wrTH THAT NAME*
FILE IS NOT TYPE 2'
TABLE FULL - PARTIAL LIST SUPPLIED*
NAME IS TOO LONG'
INVALID UNIT'
NO ROOM'
ARGUMENT ERROR'
SYMBOLIC VARIABLES'
STRING VARIABLES' '
ARRAY VARIABLES'*
LINE NUMBERS'
NULL LIST' *
Number 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 31
156
32B9
00000000015045
BASEl
DB
0/0 / 0/0/ 1/0/ 0/0 / 0/2 / 0/0/ 0/0/ 4/ 0/0/ 0/0
32 CC
08000000015050
DB
8/2 j 0< 0/ 1/6/ 0/ 0/ 0/ 3/ 2/ 0/ 0/ 0/ 6/ 4/ 0/ 0/ 1
32Dr
02080000025055
DB
2/ 8/ 0/ 0/ 2/ 5/ 6/ 0 / 0 / 5/ 1/2/0/ 1/0/2 / 4/ 0/2
32F2
00040800045060
DB
0/4/8/0/4/0/9/6/0/6/ 1/9/2/ 1/6/3/8 /4/3
3305
02070608 5065
DB
2/7/6/8
3305
5070
DlRl
D5
8
3311
5075
STACKi
DS
50
3343
5080
ADDRi
DS
2
3345
5085
PLINEl
DS
72
3381)
5090
TABLES
DS
12288
638(1
5095
END
2A00H
DH 2A00)33FF
•>
>DH 2A00-33FFF?
>DH 2A00-33FF
2 A£ 0
21
42
33
F9
0E
IF
21
87
30
CD
5E
30
CD
68
30
0E
2 A10
2A20
2A30
C2
CA
21
1C
6F
A6
2A
2A
30
0E
FE
CD
09
5F
5E
21
C2
30
87
54
0E
31
2A
0A
CD
3E
21
10
09
87
20
B9
31
32
CA
36
B2
28
20
32
2A
23
FE
3A
0D
0D
B2
2A40
32
2B
0C
47
CD
0D
20
06
20
CD
0D
20
06
5F
CD
0D
2A50
20
C3
28
2A
77
A7
CD
0D
20
23
0D
C2
28
2A
CD
68
2A60
30
0E
10
21
10
31
CD
5E
30
CD
68
30
C3
0F
2A
0E
2A70
0C
21
B7
30
CD
68
30
CD
5E
30
21
91
31
CD
10
20
2 AS 0
47
CD
0D
20
FE
31
CA
A4
2A
FE
32
CA
A4
2A
FE
33
2A9 0
CA
A4
2A
CD
68
30
0E
0C
21
20
31
CD
5E
30
CD
68
2AA0
30
C3
6F
2A
E6
0F
77
CD
10
20
47
CD
0D
20
FE
0D
2 AB2
C2
93
2A
06
0A
CD
0D
20
3A
9 1
31
21
87
31
37
3F
2 AC0
CD
1C
20
D2
DA
2A
0E
19
21
C3
30
CD
5E
30
CD
68
2 AD 2
30
C3
0F
2A
06
00
0E
04
09
3E
02
BE
CA
ED
2A
0E
2 AEi3
12
21
DC
30
CD
5E
30
CD
66
30
C3
0F
2A
2B
2B
2B
2AF0
2B
0E
06
1 1
09
33
7E
12
23
13
0D
C2
F 6
2A
26
00
2B0.3
2E
00
22
43
33
06
00
0E
04
1 1
8F
33
2A
43
33
23
2 B1 0
3E
0C
BC
CA
23
2B
22
43
33
62
6B
09
EB
73
23
72
2 B2i3
C3
0C
2B
3E
FF
23
77
26
BB
2E
BB
22
A6
32
22
A8
2B3I3
32
22
AA
32
22
AC
32
21
8F
33
22
AE
32
CD
2F
30
2B4I3
AF
32
97
32
3C
EB
BE
CA
BC
2D
EB
CD
73
30
1A
32
2350
A2
32
CD
73
30
1A
32
A3
32
AF
32
A 1
32
CD
73
30
2B60
62
6B
3E
20
BE
CA
B6
2B
3E
8F
BE
C2
73
2B
3E
01
2B70
32
97
32
3E
22
BE
C2
90
2B
3A
97
32
FE
02
C2
88
2B80
2B
AF
32
97
32
C3
B6
2B
3E
02
32
97
32
C3
B6
2B
2B90
3A
97
32
FE
00
C2
B6
2B
3£
9A
BE
C2
A4
2B
CD
C8
2 BA0
2B
C3
B6
2B
3E
40
BE
D2
B6
2B
3E
5A
BE
DA
B6
2B
2BB0
CD
EA
2B
C3
B9
2B
CD
73
30
3E
0D
21
A1
32
BE
C2
2 BC0
60
2B
CD
73
30
C3
40
2B
CD
73
30
1A
32
A5
32
CD
2 BDO
73
30
1A
32
A4
32
AF
32
A1
32
2A
AC
32
22
B0
32
2BE0
CD
7A
2C
2A
B0
32
22
AC
32
C9
3E
20
32
A5
32
32
2BF0
A4
32
1A
32
AA
32
CD
73
30
3E
0D
21
A 1
32
BE
C2
2 C0O
08
2C
CD
4A
2C
C3
49
2C
62
6B
3E
2F
BE
D2
2C
2 C
2 CIO
3E
39
BE
DA
2C
2C
1A
32
A5
32
CD
73
30
3E
0D
21
2C20
A 1
32
BE
C2
2C
2C
CD
4A
2C
C3
49
2C
62
6B
3E
24
2 C30
BE
C2
3A
2C
CD
5A
2C
C3
49
2C
3E
E0
BE
C2
46
2C
2 C40
CD
6A
2C
C3
A9
2 C
CD
4A
2C
C9
2A
A6
32
22
B0
32
2C50
CD
7 A
2C
2A
B0
32
22
A6
32
C9
2A
A8
32
22
B0
32
2 C6W
CD
7A
2C
2A
B0
32
22
A8
32
C9
2A
AA
32
22
B0
32
2 C7tJ
CD
7A
2C
2A
B0
32
22
AA
32
C9
22
9C
32
EB
22
9E
2C80
32
3E
BB
32
98
32
32
99
32
2A
AE
32
22
9A
32
2B
2C9H
3A
AA
32
77
2B
3A
A5
32
77
23
23
3E
BB
77
23
77
2 CA0
23
23
23
7E
32
AE
32
3E
CC
77
23
7E
32
AF
32
3E
2 CB0
CC
77
2A
9C
32
3E
BB
BC
C2
C9
2C
BD
C2
C9
2C
2A
2 CCO
9A
32
22
B0
32
CD
75
2D
C9
2B
56
3A
A4
32
BA
CA
2CD0
32
2D
D2
FB
2C
2A
9A
32
3A
9C
32
77
23
3A
9D
32
2 CEO
77
2A
98
32
3E
BB
BC
C2
EE
2C
BD
CA
BF
2C
3A
9A
2 CFO
32
77
23
3A
9B
32
77
CD
75
2D
C9
3E
BB
2A
9C
32
2 D0O
BC
C2
18
2D
BD
C2
18
2D
2A
98
32
3A
9A
32
77
23
2 DIO
3A
9B
32
77
CD
75
2D
C9
2A
9C
32
22
98
32
5E
23
2 D20
56
EB
22
9C
32
3E
BB
BC
C2
C9
2C
BD
C2
C9
2C
C3
2 D30
08
2D
2B
56
3A
A5
32
BE
CA
41
2D
D2
FB
2C
C3
D5
2 DAO
2C
2A
AE
32
2B
2B
2B
3A
AF
32
77
2B
3A
AE
32
77
2 D50
2B
2B
2B
EB
2A
AE
32
2B
2B
2B
2B
22
AE
32
EB
3A
2 D60
AF
32
77
2B
3A
AE
32
77
22
AE
32
2A
9C
32
22
9A
2D70
32
CD
75
2D
C9
2A
9A
32
23
23
23
23
3E
CC
BE
C2
2 D80
B5
2D
23
BE
C2
B4
2D
2B
3A
AE
32
77
23
3A
AF
32
2 D9£
77
2A
AE
32
2B
2B
3A
A2
32
7/
23
3A
A3
32
77
23
2 DAC
7E
32
AE
32
3E
CC
77
23
7E
32
AF
32
3E
CC
77
2A
2 DB0
9E
32
EB
C9
2B
5E
23
56
EB
C3
7C
2D
0E
12
21
41
2 DC2
31
CD
68
30
CD
5E
30
CD
68
30
2A
A6
32
22
B0
32
2 DDE
3E
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Page 32
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
157
SYMBOLIC VARIABLES LI ME NUMBERS
A 310 340 370 7ac or*
A 310
340
370
560
705
285
80
B 330
340
360
560
705
290
830
C 350
360
370
560
705
330
340
D 460
48 0
530
532
560
350
360
370
£ 480
480
480
480
480
530
534
5 60
410
460
550
F 480
480
480
532
534
560
450
440
1 285
286
565
580
600
630
470
445
J 266
286
570
580
600
620
540
530
532
P 470
520
590
S90
610
610
640
650
560
538
660
680
620
580
600
T 400
410
690
750
680
650
X 286
430
440
445
480
480
705
710
690
670
STRING VARIABLES
AS 50
80
820
830
750
520
640
ARRAY VARIABLES
580
820
740
ZC) 305
560
560
560
560
560
560
*
560
☆
Number 44
158
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page
5ome Useful
for a Z -80
Subroutines
Assembler
BY JOHN W. CARTER
Computer Systems Technology
Memphis State University
Memphis, TN 38152
Language Overview
Many new users of microcomputer systems purchase those
systems with one predominant software objective: BASIC
programming. Such a high-level language is certainly con¬
venient and relatively powerful. However, BASIC and other
high-level languages have a distinct disadvantage in terms of
execution time and memory usage. Two major types of high-
level languages are now in common use: compilers and in¬
terpreters.
Compilers are programs which convert an entire high-level
source program into object (binary) code, and generate an
object program which is later executed without aid of the
compiler. In generating the object program, the compiler
generates and calls object subroutines when processing is
required. Repetition of these subroutines makes the object
program inefficient in terms of execution time and memory
usag;e. However, this trade-off can be more than offset by the
convenience of the high-level language.
Interpreters are programs which convert a high-level source
pro-am into object code one line at a time. That is, each line
or source code is compiled and executed individually, requir¬
ing recompilation for each execution. No object code is pre¬
served. Therefore, in order to execute such a source program,
both the source program and the interpreter must reside in
the memory space (usually RAM). This procedure is extremely
slow and consumes large quantities of memory space. A good
example of this is evident in the long looping operations of
BASIC interpreters. For example, the execution time of a
bubble sort of more than 1000 elements is formidable. You
can expect to wait as long as an hour for such a sort to exe¬
cute — depending, of course, on the data structure.
A solution to the memory and execution time inefficiency
of compilers and interpreters can be realized in many applic¬
ations through the use of assembly language programming.
Programs can be written in assembly language which would
be inappropriate for use in a high-level language; the afore¬
mentioned sort, for example. Also, assembly language pro¬
gramming opens up a whole new world of data structures,
program structures and hardware accessibility not previously
available. Using the assembler, I/O ports, analog and digital
converters, real-time-clocks and other useful hardware and
software techniques are easily accessed.
The assembler acts like a compiler, since it is one. The
primary difference between this compiler and that which
translates a high-level language, is that translation takes place
at the machine level. Each source statement is translated to a
single operation. No binary subroutines are generated (with
the exception of macro assembly), giving the programmer
total control over the program operation. The assembler re¬
sides in memory only during the compilation process. It
generates a very efficient object code which can later be exe¬
cuted without the aid of the assembler.
In order to help open up this area of programming to those
interested individuals the following subroutines are offered.
Subroutines
When writing assembly language programs the first task
involves communication between the program and the user.
In order to do so, the peripheral keyboard and display need to
be accessed, conversions between binary and ASCII must be
performed, and some simple debugging tools would be useful.
The following nine subroutines will help to fill such a need.
They are a sample of a program library of over 60 subroutines
written by this author for use in the assembly language pro¬
gramming course in Memphis State University’s Technology
Division. Access to these subroutines can keep the beginning
programmer from becoming bogged down in the process of
program debugging.
Page 34
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
159
These program segments have been coded in Z-80 assembly
language for use on the TRS-80 microcomputer. However,
these can be easily translated for use on almost any mini or
micro.
The following is a summary of the subroutines given:
Subroutine AINPUT. This subroutine will scan the key¬
board of the microcomputer for an ASCII character, and upon
the execution of a wait loop, places that character in the
accumulator and returns. The subroutine also echoes that
character to the video display by calling subroutine APRINT
prior to the return statement. This subroutine will require
modification for use on any machine other than the TRS-80.
In order to do so, design the subroutine structure such that it
places the ASCII character in the accumulator prior to the
return.
Subroutine APRINT. This subroutine is the converse of
AINPUT. It takes an ASCII character in the accumulator and
prints it on the video display device. This subroutine will also
require modification for use on any machine other than the
TRS-80.
Subroutine REGDMP. This subroutine provides a labeled
hexadecimal dump of registers A, B, C, D, E, F, H, L, IX and
IY. The technique used is by no means the most efficient in
terms of memory usage, but it is very simple to implement
and interpret. It can be placed within a program at any point
(or points) and a dump of the registers will occur at that point
in execution without affecting the contents of any of the
registers. This subroutine is not personallized to the TRS-80.
Subroutine OUT16H. This subroutine provides a hexa¬
decimal dump of the 16-bit contents of the HL register. Any
register pair can be dumped by this subroutine. For example,
the DE pair can be dumped by executing the following se¬
quence:
PUSH
HL
; save data in HL from destruction
PUSH
PP
; pp is the register pair
POP
HL
; put that pair into the HL pair
CALL
OUT16H
; dump it
POP
HL
; restore old HL data
Subroutine
OUT08H. This subroutine provides a hexadec-
imal dump of the contents of the C register. The contents of
any register can be dumped by executing the following se-
quence:
PUSH
BC
; save data in C from destruction
LD
C,r
;r is the register to be dumped
CALL
OUT08H
; dump it
POP
BC
; restore old C data
Subroutine BINASC. This subroutine converts a four-bit
binary value in the accumulator to its ASCII hexadecimal
representation, and places that ASCII character back into
the accumulator. It is used in all printing and register dumpmg
routines.
Subroutine IN08HX. This subroutine waits for and receives
two ASCII characters from the keyboard (using AINPUT) and
converts those two characters, assumed to be in hexadecimal
representation, into the 8-bit binary equivalent. The binary
value is placed in the accumulator prior to returning to the
calling sequence.
Subroutine ASCBIN. This subroutine is the converse of
BINASC. The subroutine takes as ASCII character in the
accumulator and, assuming that it is a hexadecimal value,
converts it to the equivalent four-bit binary nybble. The
resulting nybble is placed back into the accumulator prior
to the return.
Subroutine BMLT08. This subroutine was included to
enable the beginning programmer the ability to multiply 8-
bit numbers. This subroutine will multiply two 8-bit signed 2’s
complement operands and produce a 16-bit signed 2’s comple¬
ment product, using Booth’s algorithm. In order to provide
an efficient execution time, the registers were assigned as
follows: The multiplicand and multiplier are placed in the C
and D registers, respectively, prior to execution. After the
subroutine is called, the most significant byte of the product
is in the accumulator, the least significant byte is placed in
the D register. The registers can be reassigned to provide more
convenient use at the expense of execution time.
Program BMLTST. This program was written to test each
of the subroutines. The input routines are used to accept hex
operands, the multiplication subroutine then generates the
product which is consequently printed. The registers are
dumped prior to and after the multiplication routine. An
example of the printed output is as follows:
FE+FE
=
:
Fi B
C
D
E
F
H
L
IX
IV
j
2D 08
FE
FE
00
FF
00
11
4015
FFFF
1
Fi B
C
D
E
F
H
L
IX
IV
S
80 00
0004
FE
04
00
FF
00
11
4815
FFFF
j
:
44+44-
S
fi
6
C
D
E
r-
r
ri
L
IX
IV
2D
00
44
44
00
FF
00
84
4815
FFFF
fi
o
1_‘
c
D
E
F
H
L
IX
IV
12
80
44
10
E8
FF
00
84
LO
■H
,r 1“
FFFF
t
I 1210 |
•.i
The aforementioned subroutine library is available from the
author. For information concerning the remainder of the lib¬
rary, send a self-addressed, stamped envelope to the author
at 4932 Shifri Avenue, Memphis TN 38117. The complete
source list and cassette tape will be made available for a dup¬
lication and handling fee of $10. Indicate memory size in
any requests (4K, 16K, 32K).
Mr. Carter is an assistant professor of computer systems
technology at Memphis State University and is actively in¬
volved with the development of micro and mini software,
hardware systems and computer-aided instruction. Memphis
State University offers a baccalaureate degree in Computer
Systems Technology; a curriculum which emphasizes the
hardware aspects of computer systems, as well as programming
using compilers, interpreters and assemblers.
Number 44
160
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 35
3
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Page 37
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Page 38
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
163
A Fast Fourier Transform
for the 8080
BY ROBERT D. FUSFELD
16767 Marquez Terrace
Pacific Palisades, Cal. 90272
The Fast Fourier Transform (FFT) is a rapid method for
digital computer calculation of Discrete Fourier Transforms
(DFT). To begin with, the frequency spectrum of a continuous
random wave will be a continuous curve with real and
imaginary components. The imaginary components arise from
analysis of a real signal because of the mathematical necessity
of adjusting the phase relationship of the various frequency
components of the spectrum to give a true representation of
the original signal. However, when doing a digital calculation,
the signal to be analysed must be sampled at discrete intervals.
When this is done, a modification of the calculation process
known as a DFT becomes necessary. In 1964 Cooley and
Tukey (Ref. 1) developed the FFT which greatly reduces the
calculation time while giving the same numerical results as the
DFT. These results are an interval sampled approximation of
the continuous frequency spectrum. A good review of the
mathematical reasoning behind the FFT calculation is given
by Brigham (Ref. 2). Douglass (Ref. 5) also gives some useful
comments for users of the FFT.
The importance of Fourier Transforms is that spectral
analysis is an extremely valuable tool in many types of
engineering and scientific investigations. Applications occur in
electrical engineering, vibration analysis, meteorology, speech
recording and synthesis, music, etc. Naturally, due to the
widespread use, many computer programs to perform the FFT
calculation are readily available, particularly in high level
languages such as ALGOL and FORTRAN (Ref. 2). When it
comes to the microcomputer, BASIC programs are available
such as the one by Stanley and Peterson (Ref. 3). However,
in the interest of economy of memory and of computation
time, implementation of the FFT in machine language is
highly desireable. This was done for the 6800 CPU by Lord
(Ref. 4). The program listed here is a similar one for the 8080
CPU.
This program is a direct implementation in 8080 machine
language of Brigham’s flow chart for the FFT calculation
(Ref. 2, page 161). The calculation is performed on 256
points of input data and gives the power spectrum at 128 dis¬
crete points. The input data, calculations, and results are all
done in single byte, two’s complement format. This
immediately limits the precision to approximately slide rule
accuracy with two place decimal numbers. The indexing of
data addresses is simplified for the 256 points by using Lord’s
suggestion of starting all data tables and the sine table on a
page boundary. Further simplifications are made by writing
the sine table as the sine times 128. The “MULT” routine
then does a signed multiply and divide by 128. A “scale test”
and “scale” procedure is done before each pass thru the data,
during the calculation of each new data point and after cal¬
culation of power values. The number of times the real and
imaginary data tables have been scaled by dividing by two is
given in address 2277 H . However, the power values may have
been scaled even further to prevent overflow. The power
values at each discrete point are simply the sum of the squares
of the real and imaginary data at that point.
To use this FFT program the user must input his 256 points
of real data into addresses 2400 H to 24FF H and fill the
imaginary data table 2500 H to 25FF H with zeros. I use a Cro-
memco D+7AI/0 board to convert an analog signal into the
Number 44
164
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 39
correct digital two’s complement format. The next user’s
step is to “CALL FFT”. The calculation takes about twenty
seconds and is concluded with a “RET” command. The power
spectrum will be located in addresses 2600 H to 267F H . The
real and imaginary frequency spectrum values will be located
in 2400 h to 247 F h and 2500 h to 257 Fjj respectively. The
original input data in 2400 H to 24FF^ has been replaced by
the real part of the answer. The answers have been unscram¬
bled as required in the FFT algorithm at the end of the cal¬
culation. The user can display the power spectrum on an
oscilloscope, print out the data, or use it in any way necessary
for his study.
V/hat do the points on the power spectrum signify? The
first point is the relative power at zero frequency. This is the
mean offset of the original data from zero. If the total of 256
data points indicate a time span of T seconds, then the interval
between power spectrum points is 1/T Hertz. For example, if
the original data was recorded at 10,000 Hertz then the 256
point sample would span .0255 seconds. The interval between
points would then be 1/.0255 = 39.21 Hertz and the last point
would be the power at 4979 Hertz. As is well known, the
sampling rate should be at least twice the frequency of the
highest frequency component in the signal.
The FFT program listed here has been assembled at 2000 H .
The first 8K bytes of memory have been left for other uses.
The program itself occupies IK bytes and uses the next three
pages starting at 2400 H (768 bytes) for the data and power
tables. If the FFT program were to be reassembled at a dif¬
ferent address, the first seven lines of the source listing would
need to be changed. Some precautions will have to be taken.
The real and imaginary data tables must start on consecutive
O',
page boundaries, i.e., 2400 H and 2500 H . Also, “FIN” must
equate to one higher than the high byte of “IMAG”, i.e., 26 H .
Finally, the location of Til must be at K+9. The program and
sine table could be in ROM but K and the next 13 bytes must
be in RAM as well as the data and power tables.
For users who might want to compare this program with
Brigham’s flow chart (Ref. 2), abbreviations used in the
listing generally are those used in his book. However, because
many commonly used printers (including mine) do not have
lower case characters, there have been a few changes. K is used
in place of k, REAL, REAL 1, IMAG, or IMAG 1 is used in
place of Xj(k), and REAL 2 or IMAG 2 is used in place of
x^k+N/2 1 ).
References
1. Cooley, J.W. and Tukey J.W.: An Algorithm for the Machine
Calculation of Complex Fourier Series. Mathematics of Compu¬
tation 19:297-301, 1965. Reprinted in: Rabiner and Roder, Eds.:
Digital Signal Processing. IEEE Press, New York, 1972.
2. Brigham, E.O.: The Fast Fourier Transform. Prentice-Hall, New
Jersey, 1974.
3. Stanley, W.D. and Peterson, S.J.: Fast Fourier Transforms on Your
Home Computer. Byte, Vol. 3, P.14-25, December 1978.
4. Lord, R.H.: Fast Fourier for the 6800. Byte Vol. 4, P.108-119,
February 1979.
5. Douglass, K.H.: Fast Fourier Transforms on Your Home Computer.
Letter to the editor. Byte, Vol.4, P.225, May 1979.
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Oj Oj Oj Cm Oj Cm Oj Oj Oj Cm Cm Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj Oj
Number 44
168
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 43
access addend
algebra analog
application ai
level procedural language such as Pascal
or C. On the other hand, some algorithms
are particularly efficient and interesting
simply because they match the machine
structure well. Occasionally we’ll just
mention a trick, a data structure, a gim¬
mick which seems to be particularly
useful.
Merge Sort
The Merge Sort sorts a list of keys in-
place in time n*log(n). It is very simple
to state:
Recursively divide the list to be sorted in
half until sorted lists are obtained (that
is, lists of length one); then successively
merge each pair of lists until the entire
list is sorted.
A MONTHLY ALGORITHM
COLUMN
BY DENNIS ALLISON
With this issue of Dr. Dobb’s Journal
we begin a new series concentrating on
the building-blocks of systems rather
than the systems themselves. One of the
failings of most of us is the inability or
disinclination to take and use the work of
others. Everyone writes his own sort
program, his own integration program,
and so on ad infinitum. Often it would
be better and faster to take an existing
program and reuse it. Of course that is
not always possible, but often one can
take the algorithm and adapt it easily.
The intent is for this to be a reader
participation column. We will publish
submitted algorithms accompanied by
adequate, if terse, documentation and
(if possible) some measure of their
effectiveness. We certainly need a test
program drive and the results of a few
test runs. Some analysis is important.
One needs to know, for example, if a
sort program runs in time n*log(n) where
the log is base 2 or in time n'J - .
From time to time we will publish
reference lists of published algorithms.
For that reason, if you find a published
algorithm to be of use, please send it
to Algorithms, Dr. Dobb’s Journal,
PO Box E, Menlo Park, CA 94025 so it
can be added to the file. Be sure to
include a complete reference; a few
comments would also be welcome.
Lastly, if you can improve on an
algorithm published here, or if you find
a bug, we will publish corrections and
improvements. There’s a lot to be learned
about prog^imming from a study of how
algorithms are constructed.
Algorithms may be programmed in
any convenient language, including
assembler, but are preferred in a high
RECURSIVE FORM
int at 11], 1 inkC11];
sort (i,j) int i,j; -C int k, ii, jj;
if<i==j) { linkCi] = 0; return(i);}
k = i + ( < j-i )»1);
ii = sort(i,k); jj = sorttk+1,j);
return(nerge(ii,jj));
>
tierge<i,j) int i,j; { int k;
if (i==0) return (j);
if (j==0) return (i);
if(aCil>aCj]) { k = i;
else { k = j;
linktk] = nerge(i,j);
return(k);
linkti];}
linktj];>
NON-RECURSIVE FORM
Merge(i,j) int i,j; < int k,n;
k = 0;
whilet <i! =0) SS < j!=0)) {
if(ati]<aCj]) { « » i; i * j; j
n = linkCiD;
linkCi] = k;
k = i; i = «;
>
if <i==0) -C m = i; i = j; j = m; >
n = i;
while! k != 0) {
j = linktk];
linktk] = «;
« = k;
= j;
>
return(n);
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Ortnodontia, Box E. Menlo Park, CA 94025
Number 44
169
The sort is obviously n*log(n) since there
can be at most log(n) partitioning opera¬
tions and any merge operation can be, at
most, n operations long.
The program given here uses an array
of keys and an associated array of links.
The index value zero is distinguished as a
list terminator. The programming lan¬
guage is C. The routine sort returns the
index of the first element of the sorted
list, call it j. The a[j] is the first sorted
element and link [j ] is the index of the
next element, and so forth. Sort takes as
arguments the first and last indexes to be
sorted. If this is a single element (the
indexes are equal) it simply initializes the
link field and returns as a list of length
one is, by definition, sorted. If there is
more than one element, sort partitions
the list in two and calls itself to sort the
two partitioned lists and then merges
them returning the head of the merged
lists.
The merge routine merges the two
sorted lists whose heads are given as argu¬
ments and returns the head of the new
list. The data are not actually moved,
only the link fields are modified. Again
a recursive formulation is used. Only the
top elements of the two lists need be
considered. If either of the lists is empty
then the other list is the result. If not,
then one finds the index of the largest,
removes it from the sublist, and merges
the remaining values.
As written, this program is somewhat
inefficient since it uses a local variable to
save the index for the merge, and it will
recur as many times as the lists are long.
The performance can be improved by
using an iterative rather than a recursive
formulation of the merge. The procedure
is similar to the recursive one. The heads
of the two lists are examined and the
largest removed and placed on a list using
its link field to thread the list and the
procedure repeated until one of the lists
is empty. At that point the entirety of the
other list becomes the tail of the merged
list. Items from the reversed list are added
to the tail until the reversed list is empty.
At that point the merge is complete.
While this takes more code, it operates
in place with a minimum number of
procedure calls.
Number 44
170
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 45
ADVERGATE. . .
Dear Suzanne;
If you are unable to produce Dr. Dodd’s [szc] without the
advertisements, you very much should resign. In the great
muddled world of the small computer, the unbiased product
which Dr. Dodd’s [szc] Journal was prior to your editorship
is greatly needed. Another advertiser base journal is sorely
unneeded.
An example in point is your advertisement for Lifeboat
Associates. This organization represents the greatest obstacle
to small computer software development. Almost all worth¬
while CP-M products are now sold through Lifeboat. Because
of their non-support of the small dealers, these products are
not available in the computer stores. Without the support
of the computer store, most of these products are worthless.
I am strictly a user of these products and am not in any
way a dealer. I have found a great many problems in the CP-M
packages which I do use and have spent hundreds of hours
tiying to work these problems out without any local support
whatsoever. Dr. Dodd’s [szc] Journal has been a great help
in circumventing this system. Now with full page ads from
Lifeboat Associates, you can count on the fact that you
will now produce the glowing reports of these products which
are worthless.
Sincerely, Medical Central Service
Robert C. Luckey, M.D. 471 Williams, Suite 4
Richland, Washington 99352
A symptom of our times, a parable of today: guilty until
proven innocent, suspect without cause, wrong even if you’re
right. Although I’m not quite sure what Dr. Luckey is accusing
us of, it seems to be vaguely a general suspicion that, because
we now have advertising in DDJ, we are guilty... of some¬
thing, I don’t know what.
I should know, since everything that goes into this maga¬
zine filters through me: there has never been a case of altering
anything in the magazine to please an advertiser. To be honest,
our advertisers report unusually excellent response from
advertisements in DDJ, and since we limit the amount of
advertising in our pages, we don't really have to bow down to
advertisers. We haven’t done it yet, and I hope we never do.
I do have a certain way of looking at the world, and it does
not include “selling out” or going out of my way to accom¬
modate myself to another’s point of view if it does not fit
in with what I believe. It’s called “ethical. ’’Not too obsolete
a word, I hope.
I think this is really an unfair letter: it is all generalizations
and vague assumptions. Any decent graduate school in journal¬
ism would give an automatic “F” to Dr. Luckey for all accusa¬
tions/no hard data. Dr. Luckey thinks another ‘‘advertiser
base journal is sorely unneeded. ” Well, that may or may not
be true, but frankly, just between us wage-earners, I ap¬
preciate getting my very small paycheck twice a month. - SR
TABLE DRIVEN ASSEMBLER IN DDJ # 42
Dear Dr. Dobb’s :
Due to a phone call from a reader, I have become aware
of an oversight concerning the assembler. As I have been de¬
veloping a number of large programs in ML-80, I long ago
modified the compiler to substantially enlarge its internal
tables and fix a few bugs. As a result, the assembler can’t
be compiled by ML-80 as currently distributed by the CPM
User’s Group ( I have sent them the mods, but during their
year-long reorganization confusion it may be a while yet)
due to its size. The disk I am making available does contain
ML-80 with all my patches and will compile it. If I had the
source of ML-80 and I had access to a PL/M compiler, I would
have made changes that way, but I have neither. One side
effect of the changes is that the modified L82 will not run in
a 16K system. (It runs fine in 32K, with one small change it
would run in 24K, but compile smaller programs.)
Sincerely, 1522 Brockton Ave., Apt. 5
Darrel J. Van Buer Los Angeles, CA 90025
NORTH STAR PATCHES
Dear Dr. Dobb’s,
Here are some software patches for the North Star Horizon
which might prove of value to readers who use this system.
Two minor but irritating problems with North Star soft¬
ware are the use of the underline character 5FH for backspace
and the symbol for line cancel. These are useful functions
but why use printing characters? They also implement the rub-
out or delete character 7FH as a backspace. If you use their
personalization routine to change the DELECHO from 5FH to
08H, then you enable the backspace key giving you no less
than three different backspace commands. Also, you will
note that the backspace 08H will not function in DOS.
Therefore: For Release 4 Software Only
In DOS: 263C holds the backspace character; change 5FH to 08H
2637 holds the line cancel character (40H); change to
your choice. I use 7FH (rubout).
In BASIC: 48A2 holds the backspace; change 5FH to 08H
48BB holds the line cancel character; change as in DOS.
Facie 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
171
497B holds the character echo for line cancel; it con¬
tains 4 OH you do not need to change it unless you
want to.
48A6-48AA implements a backspace on rubout; if you
use the rubout for line cancel as I did, you will need
to replace these bytes with 00H.
In MONITOR: This Applies to M6700
6740 holds the backspace character, change to 08H
673B holds the line cancel character, change as in DOS.
686 A holds the character (3FH) printed after a line
cancel; this is the same character printed after an
invalid command. It is probably best to leave it alone.
This should make it possible to have a consistent set of
function keys and to regain two ‘lost’ printing characters.
Sincerely, 502 W. Kenicott
Richard M. Johnson Carbondale IL 62901
LONG AGO AND FAR AWAY
Dear Suzanne:
One of your readers pointed out a mistake in my article,
“A Floating Point Subroutine Package for the 1802” in DDJ
#37. The subroutine call addresses for floating point subtrac¬
tion (AC-OP -> AC) should be 02E9. It was printed as 029E.
Yours truly, 918 Ray Avenue
Paul Wasserman Union, NJ 07083
INCREASING Z-80 POWER
Dear Suzanne,
This is something that your readers might be interested
in which I stumbled across doing software work for a little
firm here in Sacramento. I have since found that it is not at
all well known. My favorite micro chip is the Z-80 (In fact, I
think the 8080 is completely obsolete and has been since the
first Z-80 was fabricated. So why the insistence on “8080
compatible software”? Never mind...). The basic statement
of what I discovered is that the Z-80 is far more than Zilog has
seen fit to tell us. The official tally of Z-80 instructions is 694,
according to my Z-80 tech manual. My discovery was that
about 410 instructions can be added to that total, genuine
useful instructions that any Z-80 will execute. Most involve
the twin index registers, and consist of things such as “Load
upper half of IX from any 8 -bit register” or “Load lower half
of IY immediate”. In other words, the index registers can be
used to a much greater level of efficiency than before. The
other members of the new set are things such as “Shift left
and set least signficant bit”.
The key to the new instructions came when I finally saw
something that a lot of people have probably seen: The object
code for indexed instructions can be formed by taking the
object code for an operation involving HL and tacking a 0FDH
or ODDH on at the front end (not quite, there is a problem
with the displacement byte, but to a first approximation this is
correct). What occurred to me was to try tacking those bytes
onto an instruction involving just H. So I did, and it worked!
Some notation for the following examples: HX is the high
byte of the IX register, LX the low byte, and similarly for the
IY register.
Desired
Object
Standard
instruction
code
Assembler
LD HX, A
DD 67
DEFB ODDH
LD H,A
OR LY
FD B5
DEFB 0FDH
OR L
ADD A,HY
FD 84
DEFB 0FDH
ADD A,H
You see the pattern. There are some limitations; it is not
possible, for instance, to LD HX,LY. On the other hand,
LD HX,LX is possible. The rule is that only one index register
at a time may be referenced.
The other type of additonal instructions I’ve found do not
involve the index registers. On page 50 of the Z-80 Technical
Manual, in the Op-Code column, the object codes for the
various rotate and shift instructions are defined in terms of
prototypical configurations, with the various codes being
differentiated by a 3 bit field. This means that there are 8
possible operation types. NOTE THAT ONLY SEVEN ARE
LISTED IN THE MANUAL! The missing one is pattern 6.
When it is generated, the results show a “Shift left and set
least significant bit”; i.e., the operand is shifted left and the
low bit is set rather than reset. The high bit of the operand
is shifted into the carry, and sign and parity are affected in
the expected manner. This one is moderately useful, also.
Any good macro assembler can generate these extra codes,
and in fact, the Microsoft MACRO-80 package allows a single
macro to generate all the extra index register instructions.
I am sure that other packages will also. Again. ANY Z-80 will
execute them. I am on the track of a few more. Once I get
them all, I am going to write an assembler that accepts these
extended codes. The only question now remaining is: why
didn’t Zilog tell us?
I hope the above sets someone onto a better way to accom¬
plish a project.
Sincerely, 8725 La Riviera Dr., #68
Daniel R. Lunsford Sacramento, CA 95826
A SLIGHT CORRECTION
To the Editor:
I would like to correct a slight inaccuracy in the article
“CP/M and CDOS Program Compatibility”, by Jim Warner, in
the January, 1980, issue.
The article states “The address of the jump vector table
depends on the amount of memory allocated to CP/M and
unfortunately D.R. has not specified how transient programs
should locate it.” Actually, the D.R. CP/M System Alteration
Guide, Rev. Jan., 1978, pages 17 and 21, specifies that
location 0,1,2 must contain
JMP WBOOT
where WBOOT is the address of the second entry in the jump
vector table. Contents of location 0, 1,2 are to be set in the
BIOS. See sample CBIOS, System Alteration Guide, page C-5.
Code to load a pointer to the jump vector table origin into
HL, usable in any transient program, is as follows:
LHLD 1
Number 44
172
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Page 47
DCX H
DCX H
DCX H
The article was otherwise quite informative, as was the
issue as a whole.
Yours sincerely,
Dr. Stefan M. Silverston
SAVING 8080 REGISTERS IN 47 BYTES
Dear S. R.,
In the last issue of Doctor Dobb’s the problem was pre¬
sented of saving all the 8080 registers in 58 bytes or less. This
was assuming that the stack pointer may be pointing to ROM
at the time the routine was entered. The first time the solution
was attempted the code took only 42 bytes. Either I do not
understand completely the question or someone’s coding is
not very tight. (PSW, BC, DE, HL, & the SP saved with all
renters restored at the exit)
Yours truly, 2305 W. Winona
L. Barker Chicago, Ill. 60625
pointer might not be valid. (If the stack pointer is pointing at
ROM, at memory-mapped I/O devices, or an non-existent
memory, then PUSH PSW followed later by POP PSW will not
restore the original condition codes or register A).
Also in DDJ #41: Jon Bokelman gives a clever, but overly-
complicated solution to the problem. (I will take his word for
it that his solution correctly deduces the settings of the N and
H flags).
In my solution to the problem, one of two DAD SP instruc¬
tions is executed, depending on the setting of the carry flag.
If the carry is reset when the routine is entered, then the jump
in the third instruction is not taken, and the following DAD
instruction leaves the carry reset. If the carry is set when the
routine is entered, the jump in the third instruction is taken
to SAVE1, and the carry is set by the STC instruction that
follows the DAD. In either case, when the label SAVE2 is
reached, the carry flag is the same as it was when the routine
was entered. (All other flags are also the same, since DAD
affects only the carry flag). At the end of the routine, all
registers have been saved and only HL and the stack pointer
contain values that are different from their entry values. The
original contents of these registers can be easily restored if
desired. (Where was the original statement of the problem
and what was its motivation?)
Sincerely, 5472 Playa Del Rey
Jim Howell San Jose, CA 95123
As pec Dr. Dobb's »4w page 9b.
Save all bube registers (Nuit buob not Zbv)
Assuming stack may be pointing to kOM at entry
; 5 flags
bit numbers
7 6
5 4 u
2 1
; Flags
S Z
6 AC u
P 1
0000
222D00
START:
SHLD
ADDK+b ;
save hL
00k) i
EB
XCHG
0004
2221*00
SHLD
ADDR+4 ;
save DE
0607
210006
LXI
H , 0
0 0 0 A
54
MOV
D,H
0603
5D
MOV
E, L
00 0C
D21100
JNC
SKIP
000 F
1E01
MV i
E, 1
0011
39
SKIP:
DAD
SP ;
HL=SP
601 ,2
222B00
SHLD
ADDR+b
save pointer
0015
312900
LXI
SP,ADDR+4
0018
F5
PUSH
PSW
00 r>
El
POP
H i
PSW in HL
001A
19
DAD
D
witn carry t
00 IB
C5
PUSH
b ;
save BC
061C
E5
PUSH
h ;
save PSW
00 Id
FI
POP
PSW ;
restore
001B
Cl
Pup
B
00 IP
Dl
PUP
D
0620
El
POP
H
oiq stack po
00 2 j.
Fy
SPHL
00 2 2
2A2D00
LHLD
ADDK+o ;
restore HL
.**•«**
00 2 b
ADDR :
DS
10
00 2 F
END
P0'J~
INE TO SAVE T HE STATUS OF THE 8080
NO ASSUMPTIONS ARE MADE
ABOUT THE INITIAL CONTENTS
OF
ANY OF THE REGISTERS
SAVE:
SHLD
HLSAVE
; SAVE H AND L
I.XT
H, 0
; PREPARE TO GET S~ACK
POINTER
JC
SAVE 1
; JUMP IF CARRY IS SET
DAD
SP
; GET STACK PTR, LEAVE
CARRY RESET
JMP
SAVE?
SAVE 1 :
DAD
SP
; GE~ STACK PTR
STC
; AND RESTORE CARRY TO
•SET'
HL NOW CONTAINS INITIAL
STACK POINTER
THE
CARRY FLAG (AND ALL
OTHFR REGISTERS) ARE THE SAME
j
AS
THEY WE B E ON EK“°Y
SAVE?:
LXI
SP, LCLSTK
; LOCAL STACK
PUSH
H
: SAVE INITIAL STACK POINTER
PUSH
D
; AND 0~HE B REGISTERS
PUSH
B
PUSH
PSW
... all registers are now saved ...
ORC RAM ; SOMEWHERE IN "AM
DS 20 ; LOCAL STACK (WI"H SOME EXTRA SPACE
LCLSTK FO'J *
HLSAVE DS 2
Program =37 bytes
Storage = 10 bytes
Total = 47 bytes
VARIATION ON SAVING 8080 STATUS
Dear Dr. Dobb’s,
One of the more popular topics in DDJ recently has been
how to save the status of an 8080 if no assumptions can be
made about what is in any of the registers. The major problem
is to get the stack pointer contents without altering the carry
flag. A couple of writers in DDJ #41 used the current stack to
save one or more registers, but this is not allowed by the
conditions of the problem, since the contents of the stack
Page 48
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 44
173
Dr. DoBB'S JoURNALof
COMPUTER
(Calisthenics Cf Orthodontia
Running Light Without Over byte
Number 45 May 1980 Volume 5, Issue 5
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
Special Issue!
The C R'ogramming Language
A Small C Compiler for the 8080’s 5
Ron Cain
The C Programming Language 20
D.M. Ritchie, S.C. Johnson, M.E. Lesk, B.W. Kernighan
Structured Programming, C and tiny c 30
Tom Gibson and Scott Guthery
Help with OSI’s CP/M 36
Lee Barker
MITS DOS — Disk to Disk Copy Routine 40
Andrew Bender
An 8080 to Z80 Translator System 47
Robert W. Dea
fi smFiii a anainiEN
EEfl THE SESE's
BY RON CAIN
811 Eleventh Ave.
Redwood City, CA 94063
I had to have a compiler for my home computer.
There was no doubt about it: after programming
nearly every day in BLISS and then reading about C, PASCAL,
LISP, and all the other various languages becoming available, it
made no sense at all to continue programming in assembly
language.
However, the question arose: Which language?
Surprisingly, the decision was not difficult. Since I do most¬
ly system type programming (editors, music-board drivers,
modem talkers, faster versions of LIFE, etc.) rather than
application programming (accounting programs, solar eclipse
predictors, etc.), the choice boiled down to two: C or BLISS.
Besides having the most esoteric names of the group, both
possess the strengths of system programming languages. Which
is to say they both have a slightly better notion of computer
architectures than strictly application oriented languages in
terms of accessing bytes and words, and neither wastes time
doing “garbage collection” or keeping track of legal array
subscripting. Both are intended to produce fairly fast (usually
inline) code to get the job done with the least amount of
overhead.
After looking around the marketplace, I decided C was the
appropriate choice if I expected to produce code usable by
others. However, another thing also became obvious: the C
compilers available either cost a lot of money, ran only on
CP/M, or both. Having neither a lot of money nor CP/M
(the second by choice), I had to think of an alternate
approach.
The first step came by way of the Tiny-C Interpreter
offered by Tiny-C Associates. For a mere $40, I was able
to buy the source code of a working C interpreter. I intended
to use it to run the C programs I would write until something
bigger and better came along. I sent off the money, got the
huge white notebook in the mail, and after a couple weeks of
typing, had it up and running. Let me be another of many
praising the product. The documentation, clarity of print,
and ease of implementation of the thing were all exceedingly
good.
It gave me a few weeks to evaluate the C language as well as
the interpreter. It became obvious after very little time that
the language was very easy to use and to follow. It also became
obvious that the interpreter, though an excellent
implementation, was too slow for my needs. Modem
to disk programs like to think in terms of microseconds,
not milliseconds, and the former was not to be had with
an interpreter. Clearly, a third approach was needed.
The solution was obvious. I had to write the compiler
myself. I said obvious, not easy.
So, after gathering together a thick stack of paper and
getting ready to produce the (hopefully) last vast 8080
programming effort, I wrote a few lines, and, ... recon¬
sidered.
Hmmm. What better use of a systems programming
language could there be than to write a compiler? And wliat
better language could be used than the one the compiler
would ultimately support? Ideas began to gel, and pieces
began to fit together. I already had the interpreter. Even
though it was slow, it might be just the ticket to bootstrap
my way onto the machine. And so it began.
Considering the fact I had never even seen a compiler
before and had not done any lengthy programs in C, the
thing went together in a remarkably short period of time.
Chalk that up to the ease of use of the language. The ability
to have variables local to individual routines made the
recursive-descent expression parser fit together literally in
hours. A few weeks of a couple hours a night saw the compiler
begin to take shape. A few obstacles appeared along the way;
probably the worst being the point where I discovered I didn’t
have enough memory for the entire compiler to reside in
memory along with the interpreter. One demonic session with
the editor deleting all comments (gulp), and shortening all
names, brought it to size and solved that problem. The com¬
piler’s still recovering from that early trauma. Eventually,
there came an evening when all such little problems were
solved, and the compiler, running under the interpreter,
accepted a small C program and produced an 8080 program.
At that point, I refined the compiler, removed subtle errors,
and discovered I still didn’t have enough memory for the com¬
piler, the interpreter, and the symbol table a program as large
as the compiler itself required. So I asked around, eventually
got access to a UNIX system, and spent a couple more weeks
refining the compiler without regard to memory or inter¬
preters. This exercise helped remove some of the less obvious
syntax errors not caught by the interpreter and necessitated
modifying the compiler to accept the true C syntax rather
than the slightly-modified syntax used by the interpreter.
After this upgrade, the compiler was beginning to took like a
true C compiler, and there came a time it ran under UNIX and
accepted as input itself.
So, finally, I was able to take the equivalent 8080 code for
the compiler back to my machine at home to complete it. The
generated code was assembled, run, and once again the com-
Number 45
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 5
piler was submitted to itself. The results of this inbreeding
highlighted errors in the generated 8080 code which had thus
far been hidden. I set those aright, compiled the compiler
once again, then used the ouput to compile the compiler
again, and then one more time (sound like an infinite loop?)
compiled the compiler. When the code generated by this
great-grandson was byte-for-byte identical to the code
generated by UNIX way back when, and all subsequent
offspring produced such twins, I decided the thing could
be considered working.
Once it was working, I decided it would save people in a
similar situation a lot of parallel effort if I made the thing
available. And if I sold it, I would probably get caught up in
supporting it on a number of machines, which was not my
intention behind writing it. Giving it away for free seemed like
an excellent way to make C available to hobbyists who might
otherwise not have been able to get it. What better way to add
users to the C community? So here it is.
For those of you who are interested in getting a compiler
for a structured language on your home machines, I’d feel
flattered if you’d consider the one published here. And if you
are the sort who is looking for a systems programming
language, you are undoubedly the sort who would modify the
thing to fit your own needs. Therefore, a few vital statistics are
in order.
In a nutshell, the compiler:
1. Is written in C.
2. Accepts as input a text file written in C.
3. Produces as output a text file of 8080 mnemonics.
The syntax it accepts is a subset of the standard C language.
Within this subset, it does not depart from the standard
syntax, which means the listing shown here will compile and
run under UNIX. Although the subset is limited to make the
compiler simpler and will therefore not accept just any pre¬
existing C program, the programs you can write with it are
authentic and will be compatible with more complete
compilers.
Right out front, so that UNIX freaks can groan and keep
their hopes from getting too high, let me tell you the features
of standard C this compiler does NOT support:
1. Floating-point data types.
2. Structures (or unions).
3. Multiple dimension arrays.
The aim was not to support the full C language, but rather
to support enough of a subset to be able to create C programs
which would be compatible with standard C. Then, as the
compiler expanded, more and more features could be added to
bring it closer to the real thing.
Currently, the allowable data types are:
1. char—8 bit data element.
2. int —16 bit data element.
Obviously, this means the compiler is an integer-only
subset of the language. Which means it will not handle
floating-point numbers. Actually, all internal arithmetic
operations assume 16-bit integers, meaning 8-bit character
elements are sign-extended prior to use.
Allowable modifiers of the two basic types are:
1. type *name — declares name to be a pointer to an element
of the specified type.
2. type name [ ] —syntactically identical to the above pointer
declaration.
3. type name [constant] —declares an array of “constant” size
where each array element is of the specified type.
If you’ve worked with C before, you know just about
everything is done with pointers. It lets you exploit the archi¬
tecture of the cpu by giving access to all addressable memory.
Unlike standard C, you can’t use more than one modifier per
declaration, meaning it will not accept something like “int
(*name) [ ] ”. This does not present a terrible restriction,
but it must be mentioned. Since no runtime checking is made
on the legality of pointer usage, it is a trivial matter to access
any byte in memory, and a not-at-all-trivial problem finding
which routine is clobbering some random location. You can
see why pointers have been lumped with “goto’s” as the bane
of the code maintainers and modifiers.
Allowable primary expressions are:
1. A local or global variable name. Any name which has been
declared previously may be used as an expression. The
name can be any length, but only the first 8 characters are
used by the compiler. Presently, variable names are not
folded to upper-case prior to being used in the output file.
Therefore, the variable “x” would expand in the expression
“x = 0” to:
LXI H,0
SHLD x
If the assembler you intend to use cannot handle lower¬
case names, do not use lower-case names in your C
programs.
2. Constants. These can be either:
a. A decimal number.
b. A single or pair of ASCII characters enclosed in single
quotes, such as ‘a’ or ‘TX’.
c. A string enclosed in double quotes, such as “this is
a string”. The value such a constant yields is a pointer
to the first character of the string which the compiler
stores in memory.
3. Function calls. These are defined as any expression
followed by an open paren. Thus, a function can be to a
named routine, such as “print()”, or to the results of
some expression, such as “ 1000()” (which calls location
1000 decimal), or “array [i]()” which calls the location
whose value is found in array [i]. Functions always return
a value in HL, though it does not have to be used. Argu¬
ments to functions appear between the parentheses and are
pushed onto the stack in the order they appear. Hence,
“print(x,y,z);” would effectively do:
PUSH x
PUSHy
PUSH z
CALL print
Any number of arguments may be passed.
4. Subscripted elements. Either an array name or a pointer
may be subscripted to refer to the appropriate element.
Subscripts are assumed to start from zero. Therefore, legal
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Or. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
177
expressions are:
array [0] - the first element in array,
array [x + 31] — the element at the address given by
adding x to 31 and then to array,
pointer [i] — the element at the address given by
adding i to the contents of pointer.
Only single dimensions are allowed. Subscripting either an
integer array or a pointer to an integer will cause the sub¬
script expression to be doubled. Therefore, if you declare
“int *ptr”, the expression “ptr[3]” refers to the element
at ptr+6.
Allowable unary expression operators are:
1. — forms the two’s complement of the expression
(minus).
2. — refers to the element pointed to by the expression
(providing the expression is a pointer).
3. “&” — evaluates the address of the given expression,
providing it has one. Hence, &count yields the
address of the element “count”. &1000 is an
error.
4. increments the expression by one. If this appears
before the expression, it increments before using
it. If it appears after it, it will increment it after.
Only lvalues (expressions which can appear on the
left-hand side of an equal sign) are allowed.
Hence, assuming “count” contains a 5, ++count
would evaluate to a 6, and “count” would contain
a 6. Count++ would evaluate to a 5, and count
would contain a 6. 1000++ is illegal. If this
operator is applied to an integer pointer, it will
increment by 2.
5. — decrements the expression by one. This works just
like ++ but subtracts one rather than adding.
Allowable binary operators are:
44 99
M# »*
44 l 99
“%”
6. “I”
7
8.
9 «=”
1 .
2 .
3.
4.
5.
adds the two expressions (i.e. count + total)
subtracts the two expressions,
multiplies the two expressions,
divides the first expression by the second,
yields the remainder after dividing the first expres¬
sion by the second (modulo),
yields the logical inclusive “or” of the two expres¬
sions.
yields the logical exclusive “or”,
yields the logical “and”.
assigns the value of the expression on the right to
the one on the left. Since evaluation is done right
to left in this case, syntaxes like:
x = y = z = 0;
are legal.
Comparison operators compare two expressions and yield
either a zero or a one depending whether the result of the
compare is false or true, respectively. These include:
1. tests for equality.
2. tests for inequality.
3. “<” — tests for less than.
4. “>” — tests for greater than.
5. “<=” — tests for less than or equal to.
Comparisons involving a pointer (which is an address) are
done as unsigned compares. All other compares are signed.
Program control is accomplished by the following allowable
statements:
1. expression; An expression, no matter how complex, is con¬
sidered a simple statement.
2. if (expression) statement; If the expression is nonzero, the
statement is executed, otherwise it isn’t.
3. if (expression) statement; else statement; This form of the
“if” statement allows the “else” clause. As is the case with
most “dangling else” ambiguities, all “else’s” pair with the
nearest unmatched “if’.
4. while (expression) statement; The statement is performed
until the expression becomes zero. Since the test is made
before the statement is executed the first time, it need not
be executed at all.
5. break; This statement will cause control to be transferred
out of the inner-most “while” loop.
6. continue; This statement, used within a “while” loop,
will transfer control back to the top of the loop.
7. return; This statement does an immediate return from the
current function. If a function does not end with this
statement, one is performed regardless.
8. return expression; This statement allows a function to
return a value explicitly.
9. ; A semicolon by itself is considered a null statement which
does nothing but take the place of a statement. You see this
in forms such as: “while ( *iptr++ = *jptr++) ;” where the
test itself contains all the necessary parts of the statement.
10. {statement; statement;...; statement;} The use of curly
brackets (“ { } ”) around any group of simple statements
is considered a compound statement. A compound state¬
ment can be used anywhere a simple statement can. For
example:
while (1) (x = 3; y = 10; funct(33);}
or
if (x < y)
{ print(x);
total (x);
else
{ type (“all done”);
x = y;
}
The compiler also accepts some pseudo-op type statements.
These are:
1. #include filename Anywhere this statement appears in the
program, the indicated filename will be opened and
inserted. The “included” file may not contain an “#include”
statement.
2. #define name string This statement will cause the given
name to be replaced by the string throughout the entire
program. Normally, it is used to define constants, such as:
#define tablesize 1000
#define maxlength 8
But it can also be used for any sort of text:
# define jprint 3crs print (12); print(12); print(12);
Number 45
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
The replacement is purely on a text level, and error
checking will be performed only after the replacement.
3. #asm ... #endasm This structure is not supported by
standard C, but it was a feature I felt I needed. It may
appear anywhere a statement would, but it passes every¬
thing between the word “#asm” and the word “#endasm”
right through the parser without intervention. It is intended
to be used to pass assembly language code through the
parsing mechanism. Since it counts as a single statement,
allowable (and expected) forms are:
if (x < y)
#asm
LHLD TOTAL
CALL ADD
CNCERROR
#endasm
else return;
This pseudo-op conceivably allows an entire assembly
language program to be passed through the compiler. Its
intent is to allow machine dependent features (like the
8080’s “IN” and “OUT” instructions to be used without
writing separate programs).
In parsing the input, the compiler never tries to be overly
clever, which simplifies the compiler quite a bit and makes
the generated code quite predictable, if somewhat redundant.
The input file is scanned character-by-character left to
right. Only a single 80 character line at a time is buffered. This
reduces the amount of memory used by the compiler and
makes any kind of look-ahead improbable. The expression
parser (namely the routines heir 1 () through heir 11 () and
primary()) uses the method of recursive-descent to evaluate
an expression, which means the routines call themselves when
necessary (such as encountering an open paren). All expres¬
sions result in a value in the HL register pair. Character values
are sign-extended through the H register. This means the
line of code:
x : = 5;
generates the code:
LX I H, 5
SHLDx
Notice, HL still contains the 5. The compiler relies upon this
convention in the forms:
x : = y = z = 0;
which generates the code:
LX I H,0
SHLDx
SHLDy
SHLDz
In fact, using an expression as a statement is a good way to
load the HL pair using the compiler. The expression:
100 ;
puts 100 into the HL pair. Of more use might be the expres¬
sion:
& local;
which would load the address of the variable “local” into HL.
Whenever a binary operator is seen, and a second value is
needed, the HL pair is pushed onto the stack, and the second
operand is loaded into HL. Therefore, the expression:
x = x + 5;
would generate the code:
LHLD x
PUSH H
LXI H,5
POP D
DADD
SHLDx
Obviously, this shows the excessive caution used by the
compiler. It need not actually have pushed the HL pair, but
could merely have put it into DE with an “XCHG” instruc¬
tion. Except for the one fact the compiler had no idea how
involved the second expression would be. Consider:
x = x + (5 * x) / funct(x * 3);
Obviously, in such a case, pushing H would be wise. The
compiler makes no distinctions, but generates bullet-proof,
rather than optimal, code.
Global variables (those declared outside of a function) are
assigned storage and can be referenced by name. This means
assembly language code can refer to the global variables using
the same name as the C program. Local variables, however,
like function arguments, occupy a spot on the stack, and are
referenced by some offset from the current stack pointer.
The simple routine:
main(arg)
char arg;
{int localword;
localword = arg;
would generate the code:
main:
PUSH B
LXI H,0
DAD SP
PUSH H
LXI H,4
DAD SP
CALL ccgchar
POP D
CALL ccpint
POP B
RET
Notice a few important items. First, the address of
“localword” is evaluated as it is encountered. Then it is
pushed, since HL must be used for something else. The address
of “arg” is evaluated, and an outside routine “ccgchar” is
called to read one byte from the specified address and to sign-
extend it. Then the address of “localword” is popped, and
another routine “ccpint” is called to store a 16-bit value in
HL at the address in DE. This means there is a runtime library
needed for the C programs produced by this compiler. It is
not listed here, since it is as long as the compiler itself (it is
in 8080 code) and all the routines seemed fairly obvious,
since they are all invoked by the code generating routines at
the end of the compiler. If there is enough response, perhaps
Dr. Dobbs can print that too one day.
I guess the biggest question remaining is “How can I get it
on my system?”
Good question, and I’m afraid you know the answer better
than I do.
Obviously, the C listing printed here is not directly usable
on your home system. If you had access to a UNIX system,
Page 8
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
179
you could simply type it in as shown, compile it with UNIX’s
C compiler, and have a running version. At that point, you
could run the compiler under UNIX, submit it to itself for
compilation, and the output would be a copy of the compiler
in 8080 mnemonics. That output is directly usable on any
8080 machine with some mass-storage and an assembler.
This is just what I did in bootstrapping the compiler, so
naturally I have all the intermediate files on floppy disk.
However, I am not a distributor. I can’t handle, nor do I
want to handle, requests to put the files onto some other
media. I originally released the first version of the compiler
some months ago and have not been able to deal with even the
moderate number of requests.
It is my hope some of you will either go to the effort
yourselves or get some distributor to go to the trouble of
getting the files onto the necessary floppies or cassettes. Such
group efforts I will assist where possible.
Already, a couple of distributors or private parties have the
thing working on other machines or are planning it.
Walt Bilofsky, Software Consultant, 14478 Glorietta Drive,
Sherman Oaks, Ca. 91423, has been in on this thing from early
on, and has an extremely improved version running on his
Heath-kit. His compiler supports much more of the standard
C language, and his runtime library sports the ability to do
I/O redirection like the UNIX shell. I am told he is considering
a CP/M version, and will eventually support others. What is
published here is free, if difficult to transport directly to your
system. But for a small fee, I’m sure he’ll be able to supply
you with a working compiler.
Also, The Code Works has obtained a version and was
considering making it work on other machines. Their address is
Box 550, Goleta, CA 93017.
Which brings up interesting points. If you haven’t already
made the intuitive leap about the power behind writing the
compiler in the same language it supports, it lies in the ability
to compile itself. This means a user with extra memory can
add additional features to the basic compiler, compile it with
the old compiler, and voila! A new and more powerful version
will exist.
If you have a working compiler on one cpu and want to
bootstrap your way to another kind of processor, you need
only change the code generating portions of the compiler
(all grouped into the final section of the listing) to make code
for the new machine, compile that compiler, and once again,
you have a new beasty. Sort of like cloning.
Personally, I’ve developed the thing about as far as I need
to begin using it for the things I originally intended. After all,
I did write it for a reason. However, I am still interested in
hearing what modifications are found useful, what machines
it eventually wanders onto, and any other interesting paths
this thing takes.
If you get this thing running on your home system, make
mods to it, make it run on another cpu, or are in a position to
make copies of your work for others with similar cpu’s, I
would appreciate hearing about it in Dr. Dobb’s.
I thing it’s an excellent opportunity to leam how a com¬
piler works and at the same time establish the necessary
groundwork for a C community. It’s already here, with the
Tiny-C interpreter and the other C compilers now available.
I hope to see alot more C programs in the future.
PNESNFlfll
. ... .
/• V
/* small-c compiler */
/* rev. 1.1 */
/* by Ron Cain */
/* */
/**.......
/* Define system dependent parameters */
/* Stand-alone definitions */
/• {Jdefine NULL 0 */
/* #define eol 13 */
/* UNIX definitions (if not stand-alone) */
{{include <stdio.h>
{(define eol 10
/* Define the symbol table parameters */
{{define symsiz 14
{{define symtbsz 5040
{{define numglbs 300
{{define startglb symtab
{{define endglb startglb+numglbs*symsiz
{{define startloc endglb^synsiz
{{define endloc symtab+symtbsz-symslz
/* Define symbol table entry format */
{{define name 0
{{define ident 9
{{define type 10
{{define storage 11
{{define offset 12
/* System wide name size (for symbols) */
{{define namesize 9
{{define namemax 8
/* Define possible entries for "ident" */
{{define variable 1
{{define array 2
{{define pointer 3
{{define function 4
/* Define possible entries for "tvoe" */
{{define cchar 1
{{define cint 2
/* Define possible entries for "storage" */
{{define statik 1
{{define stkloc 2
/* Define the "while" statement gueue */
{{define wqtabsz 100
{{define wqslz 4
{{define wqaax wq»wqtabsz-wqsiz
/• Define entry offsets in uhile queue */
{{define wqsym 0
({define wqsp 1
{{define uqloop 2
{{define uqlab 3
/* Define the literal pool */
tfdefine litabsz 2000
{{define litmax litabsz-1
/* Define the input line */
{{define llnesize 80
{{define linemax linesize-l
{{define rapmax linemax
/* Define the macro (define) pool */
{{define nacqsize 1000
{{define raacmax macqsize-1
/* Define statement types (tokens) */
{{define stif 1
{{define stwhlle 2
{{define streturn 3
{{define stbreak 4
{{define stcont 5
{{define stasis 6
{{define stexp 7
/* Now reserve some storage words */
Number 45
180
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 9
cheir symtabtsynitbs23;
char *glbptr,*locptr;
ini: uqCuqtabszl;
int *uqptr;
char litqClitabszJ;
int litptr;
char macqLmacqsizel;
int macptr;
char linetlinesizel;
char mllneClinesizeD;
ini: lptr/inptr;
/* Misc storage *
int nxtlab, /
litlab, /
sp, /
argstk, /
neap, y
errcnt, y
eof, y
inputs y
output/ y
input2/ y
glbflag/ y
ctext/ y
cmode, y
/* symbol tatle */
/* ptrs to next entries */
/* uhile queue */
/* ptr to next entry */
/* literal pool */
/* ptr to next entry */
/* macro string buffer */
/* and its index */
/* parsing buffer */
/* temp macro buffer */
/* ptrs into each */
Hhile(J—)
(outdec((litqCk*+DU27));
if ((J==0) I (k>=litptr))
Cnl();
break;
}
outbyte(', ');
)
Dump all static variables
need <cr> */
separate bytes */
dumpglbsf)
C
next avail label ft
label ft assigned t
compiler relative
function arg sp •/
ft open compound st
ft errors in compil
set non-zero on fi
iob ft for input fi
iob ft for output f
iob ft for "include
non-zero if Intern
non-zero to interm
non-zero uhile par
zero uhen passing
last executed stat
o literal pool */
stk ptr */
atements */
atlon */
nal input eof */
le */
ile (if any) •/
" tile */
al globals */
lx c-source •/
sing c-code */
assembly code */
ement type */
int );
ifCglbflag==0)return; /* don't if user said no */
cptr=startglb;
uhile(cptr<glbptr)
Clf(cptrCidentll=function)
/* do if anything but function */
(outstr(cptr);col();
/* output name as label... */
defstorageC); /* define storage */
j=((cptrtoifset]&255)«
((cptrCoffsetM3fc255)<<8));
/* calc ft bytes */
if((cptrCtypel==clnt)|
(cptrCidentl==pointer))
quotet 2 3; /* literal stri
*cptr; /* uork ptr to
*iptr; /* uork ptr to
>>»> start ccl ««<<
Compiler begins execution here
literal string for */
uork ptr to any char buffer */
uork ptr to any int buffer */
outdec(j);
nl();
)
cptr=cptr*symsiz;
>
Report errors for user
need that many */
errorsummary()
(
glbptr=startglb;
locptr=startloc;
uqptr=uq;
macptr =
litptr=
sp =
errcnt=
eof =
input=
input2=
outputs
ncmp=
/* clear global symbols */
/* clear local symbols */
/* clear uhile queue */
/* clear the macro pool */
/• clear literal pool */
/• stack ptr (relative) */
/* no errors */
/* not eof yet */
/* no input file */
/* or include file */
/* no open units */
/* no open compound states */
/* see if anything left hanging.•• */
if (ncmp) error("missing closing bracket");
/* open compound statement ... •/
nl();
comment( );
outdec(errcnt); /* total ft errors */
outstr(" errors in compilation.");
nl();
Get options from user
lastst= /* no last statement yet
quoteC13=
o; /* .
quoteC03='"';
cmode=l; /• en
/*
/* compiler body
/*
ask();
openout();
openin( );
header();
parsed;
dumplits( ) ;
dumpglos();
errorsummary ();
trailer();
closeout();
return;
)
...all set to zero.... */
/* fake a quote literal */
enable preprocessing */
*/
dy */
*/
/* get user options */
/* get an output tile */
/* and initial input tile */
/* intro code */
/* process ALL input */
/* then dump literal pool */
/• and all static memory */
/* summarize errors •/
/* follou-up code */
/* close the output (if any)
/* then exit to system */
int k,nuaCll;
killO;
outbyt e(12);
nl();nl();nl();
/* clear input line */
/* clear the screen •/
/* print banner */
/* Process ail input text */
/* */
/* At this level/ only static declarations/
/*
/*
parse()
defines/ includes, and function */
definitions are legal.•• */
uhile (eot==0)
<
/* do until no more input
if(amatch("char",4))(declglb(cchar);ns();>
else if(anatch("int",3))(declglb(cint);ns();>
else if(matchC’ftasm"))doasm();
else if(match("ftinclude"))doinclude();
else if(match!"ftdefine"))addmac();
else neufuncO;
blanks!); /* force eof if pending */
i
/* Dump the literal pocl */
/*
dump 1 i ts( )
(Int
It (Utptt==0) return; /* It nothing there, exit...*/
printlabel(litlab);col(); /* print literal label */
k= 0 ; /* init an index... •/
uhile (k<lltptr) /* to loop with •/
IdefbyteO; /* pseudo-op to define byte /
j=10; /* max bytes per line */
pl(" * * * small-c compiler * * *");
nl();
pl(" by Ron Cain");
nl( );nl();
/* see if user uants to interleave the c-text */
/* in form of comments (for clarity) */
pl("Do you uish the c-text to appear? ");
gets(line); /* get ansuer */
ctext=0; /* assume no */
if((ch()=='¥')I(ch()=='y'))
ctext=l; /* user said yes */
/* see if user uants us to allocate static */
/* variables by name in this module */
/* (pseudo external capability) */
pl("Do you uish the globals to be defined? ");
gets(line);
glbflag=0;
if ((ch() = ='Y')|(ch()=='y'))
glbflag=l; /* user said yes */
/* get first allouable number for compiler-generated */
/* labels (in case user uill append modules) */
uhile!1)
Cp1("Starting number for labels? ");
gets(line);
if(ch()==0)CnumC03=0;break;)
if(k=number(num))break;
)
nxtlab=numC0l;
litlab=getlabel(); /* first label=literal pool */
kill!); /* erase line */
>
/* */
/* Get output filename */
/* */
openoutO
(
kill!); /* erase line */
output=0; /* start uith none */
p1("Output filename? "); /* ask...*/
gets(line); /* get -n filename */
if(ch()==0)return; /* none given.•• */
if((output=fopen(line/"u"))==NULL) /* if given, open */
(output=0; /* can't open */
error("0pen failure");
/* erase line */
/* start uith none */
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Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
181
/* erase line */
Get (next) input tile
openin()
C
input=0; /* none to start with */
while (input==0) /* any above 1 allowed */
(kill!); /* clear line */
if(eof )break; /* if user said none */
plC'Input filenaae? ");
gets(line); /• get a name */
if(ch()==0)
(eof=l;break;3 /* none given*.• */
if (( input = fopen( line,"r"))==NULL)
(input=0; /* can't open it */
pl("Open failure");
}
>
kilK); /* erase line */
)
*/
Open an include file */
V
do include()
(
blanks!); /* skip over to nane */
i f (( input2=f open( 1 ine«-lptr,"r") ) = = NULL)
(lnput2=0;
errorC'Open failure on include file");
)
klllO; /* clear rest of line */
/* so next read will cone fron */
/* new file (if open */
/• Close the output file */
/* */
closeout!)
( if(output)fclose(output); /* if open, close it */
output=0; /* mark as closed */
)
/* */
/* Declare a static variable */
/* (i.e. define for use) */
/* */
/* makes an entry In the symbol table so subsequent */
/* references can call synbol by name */
declglb(typ) /* typ is cchar or cint */
int typ;
{ int k,j;char snameCnamesizel;
while!1)
(whiled)
(if(endstO)return; /* do line */
k=l; /* assume 1 element */
if(match!"*")) /* pointer ? */
j=pointer; /* yes */
else J=variable; /* no */
If (syraname(sname)==0) /* name ok? */
illname!); /* no... */
if(findglb(sname)) /* already there? */
■ultidef(sname);
if (matchC'C")) /* array? */
(k=needsub(); /* get size */
if(k)J=array; /* I0=array */
else J=pointer; /* 0=ptr */
)
addglb(sname,J,typ,k); /* add symbol */
break;
>
if (match(",")==0) return; /* more? */
)
>
/* V
/* Declare local variables */
/* (i.e. define for use) */
/* V
/* works Just like "declglb" but modifies machine stack */
/* and adds symbol table entry with appropriate */
/* stack offset to find it again */
declloc(typ) /* typ is cchar or cint */
int typ;
(
int k,j;char snaoeCnaaeslze);
uhlle(l)
(whiled)
(if(endst())return;
if(match("*"))
j=pointer;
else J=variable;
if (symname(snaree)==0)
lllnameO;
if(findloc(sname))
aultidef(sname);
if (matchC'C"))
(k=needsub( );
if (k)
(J=array;
if(typ==cint)k=k*k;
)
else
(J=pointer;
else
it((typ==cchar)
&(jl=pointer))
k=l;else k=2;
/* change machine stack */
sp=modstk(sp-k);
addloc(sname,J,typ,sp);
break;
)
if (uatch(",")==0) return;
>
)
/* >>»» start of cc2 <«<«« */
/• •/
/* Get required array size */
/• */
/• Invoked when declared variable is followed by "C" */
/* this routine makes subscript the absolute */
/• size of the array* */
needsub()
(
int nunCli;
if(iratch("D"))return 0; /* null size •/
if (number (nuni) = = 0) /* go after a number */
(errorC'must be constant"); /* it i
nucC0]=l; /* so to
)
if (numC03<0)
(errorC'negative size illegal");
nunC 0] = (-numC03);
>
needbrack("3"); /* force single
"); /* it isn't */
/* so force one */
/* force single dimension
return numC03; /* and return size */
)
/* */
/* Begin a function */
/* */
/* Called from "parse" this routine tries to irake a function */
/* out of what follows* */
newfuncd
(
char ntnamesize3,*ptr;
if (symname(n)==0)
(error("illegal function or declaration");
ki11(); /* invalidate line */
return;
)
if(ptr=findglb(n)) /* already In symbol table ? */
Cif(ptrCident3!=function)multidef(n);
/* already variable by that name •/
else if(ptrCoffset3==function)multidef(n);
/* already function by that name */
else ptrCoffset3=function;
/* otherwise we have what was earlier*/
/* assumed to be a function */
)
/* if not in table, define as a function now */
else addglb(n,functionsint,function);
/* we had better see open paren for args... */
if (match("(")==0)error("n.issing open paren");
outstr(n);co1();nl(); /* print function name */
argstk=0; /* init arg count */
while(match(")")==0) /* then count args */
/* any legal name bumps arg count */
(if(symname(n))argstk=argstk*2;
else(error("illegal argument name");Junk();)
blanks!);
/* if not closing paren, should be comma */
if(streq(llnedptr,")")==0)
(if(match(",")==0)
error ("expected comma"); j O'*-*
3
if(endst())break;
)
1ocptr-start loc; /* "clear" local symbol table*/
sp=0; /* preset stack ptr */
while!argstk)
/* now let user declare what types of things */
/* those arguments were */
(if(araatch("char",4))(getarg(cchar);ns();)
else if(aroatch("int",3))(getarg(cint);ns();>
e1se(error("wrong number args");breakj)
>
if(statenent()!=streturn) /* do a statement, but It */
/* it's a return, skip */
/* cleaning up the stack */
(modstk(0);
ret( );
)
sp=0; /* reset stack ptr again */
locptr=startloc; /* deallocate all locals */
3
/* */
/* Declare argument types */
/* V
/* called from "newfunc" this routine adds an entry in the */
/* local symbol table for each named argument "/
getarg(t) /* t = cchar or cint */
int t;
(
char nCnamesize3/c;int J;
reset stack ptr again */
deallocate all locals */
Number 45
182
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 11
C1 f ( argstk==0)return; /* no more args */
if(match("* M ))J=pointer;
else J=variable;
if (symname(n)==0) illnameO;
if(findloc(n))multidef(n);
if(natch("t")) /* pointer ? */
/* it is a pointer, so skip all */
/* stuff between "C3" */
Cwhile(inbyte()!=*3*)
if(endst() )break;
J=pointer;
/* add entry as pointer */
i
addloc(n,J,t,argstk);
argstk=argstk-2; /* cnt down */
if(endst())return;
if(aatch(",")==0)error("expected comma");
)
/* (for "break" statement) */
printlabe I (wqCwqloopl);col ();nl(); /* loop label */
test(wqCwalabD); /* see if true */
statement); /* If so, do a statement */
jump(wqCwqloop)); /* loop to label */
printlabel(wqCwqlab));col();nl(); /* exit label */
locptr=wqCwqsym3;
sp=icodstk(wqCwqspD);
delwhilef);
)
/* deallocate locals */
/* clean up stk ptr */
/* delete queue entry */
"return" statement
doreturnf)
(
/* if not end of statement, get an expression */
if(endst()==0)expression();
modstk(O); /* clean up stk */
ret(); /* and exit function */
/* Statement parser */
/* */
/* called whenever syntax requires */
/* a statement- */
/* this routine performs that statement */
/* and returns a number telling which one */
statement()
t if ((ch()==0) & (eof)) return;
else it(amatch("char",4))
(declloc(cchar);ns();)
else if(amatch("int",3))
(declloc(cint);ns();>
else l£(match("("))corapound();
else if(amatch("if",2))
(doif();lastst=stif;>
else if(amatch("while",5))
(dowhile();lastst=stwhile;)
else i f (aroatchC'return", 6) )
(dor eturn();ns();lastst=streturn;)
else if(araatch("break",5))
(dobreak();ns();lastst=stbreak;}
else it(amatch("continue",8))
(docont();ns();lastst=stcont;>
else if(match(";"));
else if (aatch("£asm") )
(doasm();lastst=stasra;)
/* if nothing else, assume it's an expression */
else(expresslon( );ns();lastst=r.texp;)
return lastst;
)
/* */
/• Semicolon enforcer */
/* •/
/* called whenever syntax requires a semicolon •/
ns() (if(Batch(";")==0)error("missing semicolon");)
/• */
/* Compound statement */
/• •/
/* allow any number of statements to fall between "()" */
compound( )
(
♦♦neap; /* new level open */
while(aatch(")")==0)
if(eof) return;
else stateaentO;
—neap; /* close current level */
—neap;
)
"it" statement
int flev,fsp,flabl,flab2;
flev=locptr; /* record current local level */
fsp=sp; /* record current stk ptr */
flabl=getlabel(); /* get label for false branch */
test(flabl); /* get expression, and branch false */
statementO; /* if true, do a statement */
sp=modstk(fsp); /* then clean up the stack */
locptr=flev; /* and deallocate any locals */
if (amatch("else",4)==0) /• if...else ? */
/• simple "if"...print false label */
(printlabel(flabl);col();nl();
return; /* and exit */
)
/* an "if...else" statement. */
juap(flab2=getlabel()); /* Jump around lalse code */
printlabel(Llabl);col();nl(); /* print false label */
stateaent(); /* and do "else" clause */
sp=modstk(fsp); /* then clean up stk ptr */
locptr=flev; J* and deallocate locals */
printlabel(flab2);col();nl(); /* print true label */
>
•/
"while" statement */
*/
dowhileO
(
int wqC4J;
wqCwqsya)=loeptr;
wqtwqsp]=sp;
wqCwqloop)=getlabei();
wqCwqlab)=getlabel();
addwhile(wq);
allocate local queue */
record local level */
and stk ptr */
and looping label */
and exit label */
add entry to queue */
"break" statement
int *ptr;
J* see If any "whiles" are open */
if ((ptr = readwhile( ))= = 0) return;
modstk((ptrCwqspl)); /* else cl
jump(ptrtwqlabJ); /* Jump to
)
) return; /* no */
/* else clean up stk ptr */
/* Jump to exit label */
/*
/*
/*
/* ente
/•
doasm( )
int *ptr;
/* see if any "whiles" are open */
if ((ptr = readwhile( )) ==0) return;
modstk((ptrCwqspD) ); /* else cl
jump(ptrCwqloop3); /* Jump to
)
*/
"asm" pseudo-statenent */
) return; /* no */
/* else clean up stk ptr */
/* Jump to loop label */
enters mooe where assembly language statement are */
passed intact through parser */
cmode=0; /* mark mode as "asm" */
while (1)
(inlineO; /* get and print lines */
if (match("Sendasm")) break; /* until... */
if(eof)break;
outstr(line);
nl ();
)
ki Il(); /• invalidate line */
cmode=l; /* then back to parse level */
>
>»>> start of cc3 «<«<«< */
/* Perform a function call */
/• */
/* called from heirll, this routine will either call */
/* the named function, or if the supplied ptr is */
/* zero, will call the contents of HL •/
califunction(ptr)
char *ptr; /* symbol table entry (or 0) */
( int nargs;
nargs=0;
blanksO; /* already saw open paren */
if(rtr==0)push(); /* calling HL */
while(streq(]ine^lptr,")")==0)
( if(endst())break;
expressionO; /* get an argument */
if(ptr==0)swapstk(); /* don't push addr */
push(); /* push argument */
nargs=narqs^2; /* count args*2 */
if (ffatch(",")==0) break;
)
needbracxC")");
if(ptr)call(ptr);
else callstkO;
sp=modstk(sp♦nargs);
/* clean up arguments
if (an(inbyte()))
while(an(ch()))gch();
else whlle(an(ch())==0)
(if(ch()==0)break;
gch();
>
blanks();
endst()
(
blanksO;
return ((streq(1ine+lptr,";")|(ch()==0)));
illnaae()
( error("illegal symbol name");Junk();)
multidef(snarae)
char *snarae;
( error("aiready defined");
Page 12
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
183
comirent( );
outstr(snaoe);nl( );
>
needbrack(str)
char *str;
C if (match(str)==0)
(error("®issing bracket**);
coamenU ) ;outstr (str ) ;n 1 ( );
>
>
needlvalC)
( error("nust be lvalue");
)
flndglb(snane)
char ‘sname;
C char *ptr;
ptr=startglb;
uhile(ptr!=glbptr)
(if(astreq(sname,ptr,nameroax))return ptr;
ptr=ptr4symsiz;
>
return 0;
)
findloc(sname)
char *snane;
C char ‘ptr;
ptrestartloc;
while(ptrl=locptr)
(if(astreq(sname,ptr,namerBax))return ptr;
ptr=ptr+syaisiz;
addglb(snaroe,id,typ,value)
char *sname,id,typ;
int value;
l char *ptr;
if(cptr=flndglb(sname))return cptr;
If(glbptr>=endglb)
(error( "g lobal symbol table overflow*'))
return 0;
>
cptr=ptr=glbptr;
uhile( an(*ptr44- = *snaae + *)); /* copy naie */
cptrCident3=id;
cptr(type3=typ;
cptr(storage3=statik;
cptrCoffset)=value;
cptrCotfset*13=value>>8;
glbptr-glbptr+symsiz;
return cptr;
)
addloc(sname,id,typ, value)
char ‘snarne,id,typ;
int value;
C char *ptr;
if(cptr=findloc(sname))return cptr;
if(locptr>=endloc)
(error("local synbol table overflow");
return 0;
)
cptr=ptr=locptr;
while(an(*ptr*4 = ‘snarne-**))) /* copy nane */
cptrtident 3=id;
cptrCtype3=typ;
cptrCstorage J=stkloc;
cptrCoffsetDevalue;
cptrCoffset*13=value>>8;
locp tr = locptr+synslz;
return cptr;
)
/* Test if next input string is legal synbol nave */
syanarae(snane)
char ‘snarne;
( int k;char c;
blanksO;
it(alpha(ch())==0)return 0;
k = 0;
whi le(an(ch()))sna«eCk**3 = gch();
snareCk3=0;
return 1;
3
/* Return next avail internal label number */
getlabel()
( returnd+nxtlab);
)
/* Print specified number as label •/
printlabe1(label)
int label;
( outstr("cc");
outdec(label);
)
/• Test if given character is alpha */
alpha(c)
char c;
( c=c&127;
return(((c>='a•H(c<='z'))|
((c> = 'A')Mc<='Z'))|
(c=='_'));
)
/* Test if given character is numeric */
numeric(c)
char c;
f c=c4127;
return((c>='0'H(c<='9') );
)
/* Test if given character is alphanumeric */
an (c)
char c;
( return((alpha(c))I(numeric(c)));
)
/* Print a carriage return and a string only to console */
pl(str)
char *str;
( int k;
k=0;
putchar(eol);
while(strCkl)putchar(strCk**D);
)
addwhile(ptr)
int ptrCD;
(
int k;
if (wqptr==wqmax)
(error("too many active whiles");return;)
k = 0;
while (k<wqsiz)
(‘wqptr** = ptrtk**);)
>
delwhile( )
(if(readwhile()) wqptr=wqptr-uqsiz;
>
readwhi le()
(
if (wqptr==wq)(error("no active whiles" );return 0;)
else return (wqptr-wqsiz);
)
ch()
( return(lineClptr3&127);
>
nch()
( if(ch()==0)return 0;
else return(llneClptr*13&127);
1
gch()
( if(ch()==0)return 0;
else return(lineClptr443&127);
)
killC)
C lptr=0;
linetlptr1=0;
)
inbyte()
(
while(ch()==0)
(if (eof) return 0;
inllne();
preprocessO;
}
return gch();
)
inchar()
(
if(ch()==0)inline();
it(eof)return 0;
return(gchC))J
1
lnlineO
(
int k/unit;
whiled)
(if (input==0)openin();
if(eof)return;
if((unit=input2)==0)unit=input;
killO;
while((k=getc(unit))>0)
(if((k==eol)|(lptr>=linesax))break;
linetlptr4*D=k;
)
linetlptr3=0; /• append null •/
if(k<=0)
(fclose(unit);
if(input2)input2=0;
else input=0;
»
if(lptr)
(if ((ctextH(cmode))
(coiaent();
outstr(1ine);
nl();
>
lptr=0;
return;
)
)
3
/* >»>» start of cc4 <<<<<<< */
keepch(c)
char c;
( mlineCmptr3=c;
if(aptr<mpmax)mptr44;
return c;
)
preprocess( )
( int k;
char c,snameLnanesize3;
if(cffode==0)return;
Number 45
184
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 13
(
raptr=lptr=0/
uhile(chO)
tit((ch()==' ')|(ch()==9))
lkeepch(* ');
while((ch()==* ')|
(ch( )~9))
gch();
)
else if(ch()=='"')
(keepch(ch());
gcho;
while(ch()!=*"*)
(If(ch()==0)
(error("raissing quote");
break;
)
keepch(gch());
3
gch();
keepch(•"*);
>
else 1f(ch()==39)
(keepch(39);
gch();
whlle(ch()l=39)
(If(ch()==0)
(error("missing apostrophe");
break;
>
keepch(gchO);
>
gch();
keepch(39);
>
else If((ch()=='/')i(nch()=='•'))
(lnchar();inchar();
while(((ch()== # *'H
(nch()==*/*))==0)
(if(ch()==0)inline();
else lncharC);
if(eof)break;
}
inchar();inchar();
)
else lf(an(ch()))
(k = 0;
uhile(an(ch()))
(if (k<nasiemax) snameCk^+3=ch( );
gch();
}
snametk)=0;
if(k=findmac(snane) )
while (c=macqCk-* + l)
keepch(c);
else
Ck=o;
while(c=snameCk+*3)
keepch(c);
1
>
else keepch(gch());
)
keepch(O);
if(cptr>=Bpmax)error("line too long");
lp tr=raptr = 0;
while(lineClptr + 0=rollneCniptr«^3);
lptr=0;
)
( char snaneCnaoesizei;
int k;
if(symnaBe(snanie)==0)
(111name( );
kiliO;
return;
>
k = 0;
while(putmac(snaneCk++3));
while(ch()== * * | ch()== 9) gch();
while(putnac(gch() ) );
if(oacptr>=raacraax)error("raacro table full");
3
putaac(c)
char c;
( macqtroacptr3=c;
if(nacptr<niacinax)*acptr + + ;
return c;
)
flndmac(snane)
char *sna^e;
( int k;
k=0;
while(k<nacptr)
(if(astreq(sname/macq^k/nameinax))
(while(macq(k++3);
return k;
>
uhile(aacqCk++]);
while(macqCk*+3);
)
return 0;
>
outbyte(c)
char c;
if(c==0)return 0;
if(output)
(if((putc(c/output))<=0)
(c loseou t();
error("Output file error");
3
)
else putchar(c);
return c;
)
outstr(ptr)
char ptrtD;
<
int k;
k=0;
while(outbyte(ptrCk+♦)));
3
nl()
(outbyte(eol);3
tab()
(outbyte(9);>
col()
(outbyte(58);>
er ror(ptr)
char ptrC3;
C
int k;
conurent();outstr(line);nl();cottKent();
k = 0;
while(k<lp tr )
(if(lineCkJ==9) tab();
else outbyte(* *);
♦ ♦k;
)
outbyte(*“');
nl();coiraent();outstr (»•****•* ");
outstr(ptr);
outstr (" ******>•);
nl();
♦♦errent;
)
ol(ptr)
char ptrC3;
(
ot(ptr);
nl();
>
ot(ptr)
char ptrtl;
(
tab();
outstr(ptr);
}
streq(strl,str2)
char strlC3,str2C3;
(
int k;
k=0;
while (str2Ck3)
(if ((strlCkl)!=(str2Ck3)) return 0;
k ++;
)
return k;
)
astreq(strl / str2 y len)
^ char strlC3/Str2C3;int len;
int k;
k=0;
while (k<len)
(if ((strlCk3)l=(str2Ck3))break;
if(strlCk3==0)break;
if(str2Ck3==0)break;
k+^;
>
if (an(strlCk3))return 0;
if (an(str2Ck3))return 0;
return k;
>
oatch(lit)
char *lit;
(
int k;
blanks();
if (k=streq(line+lptr,lit))
(lptr=lptr+k;
return 1;
3
return 0;
>
amatch(lit/len)
char *lit;int len;
(
int k;
blanks();
if (k=astreq(line+lptr/lit/len))
(lptr=lptr^k;
whil e(an(ch()) ) inbyteO;
return 1;
3
return 0;
3
blanks()
Page 14
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
185
CuhileCl)
(while(ch()==0)
(inline!);
preprocess();
if(eof)break;
1
if(ch()== * ')gch();
else if(ch()==9)gch();
else return;
>
>
outdec(number)
lnt number;
(
int k,zs;
char c;
zs = 0;
k=10000;
If (number<0)
Cn urn be r = (-number);
outbyte(
)
while (k>=l)
C
c=nunber/k ♦ '0*;
if ((c!='0 # )|(k==l)|(zs))
Czs=l;outbyte(c);>
nuober-nunber%k;
k=k/10;
)
)
/* >»>»> start of cc5 «<«« */
expressionO
(
int lvalC2i;
if(heirl(lva1))rvalue(lval);
)
heirl( lval)
int lvalCD;
C
int k/lval2C2D;
k=heir2(lval);
if (natch("="))
Cif(k==0)(needlval();return 0;>
if (lvalC13)push();
if(heirl(lval2))rvalue(lval2);
store(lval);
return 0;
>
else return k;
)
heir2( lval)
int lvalCD;
( int k,ival2C23;
k=heir 3(lval);
blanks();
if(ch()l='|*)return k;
if (k)rvalue(lval);
whiled)
(if (natch!"I"))
(push();
if(heir3(lval2)) rvalue(lval2);
pop();
or();
)
else return 0;
helr3(lval)
int lvalCD;
C int k/lval2C2D;
k=heir4(lval);
blanks();
if(ch()1='“')return k;
if(k)rvalue(lval);
whlle(l)
Clf (match("“"))
(push!);
If(heir4(lval2))rvalue(lval2);
pop();
xor();
>
else return 0;
>
1
heir4(lval)
int lvalCD;
( int k,lval2C2D;
k=heir5(lval);
blanks!);
it(ch()l=*&')return k;
if(k)rvalue(lval);
whiled)
(if (matchC't”))
(push!);
if(heir5(lval2))rvalue(lval2);
pop();
and();
)
else return 0;
)
)
heir5(lval)
int lvalCD;
int k, lval2C 2D;
k = heir6(lval );
blanks!);
if((streg( line + lptr,"==")==0K
(streq(Iine*lptr/ M l=")==0))return k;
if(k)rvalue( lval);
whiled)
(if (match("=="))
(push();
if(heir6(lval2))rvalue(lval2);
pop();
eq()/
>
else if (match(" !=•'))
(push!);
if(heir6(lval2))rvalue(lval2);
pop();
ne( );
)
else return 0;
)
>
heir6( lval)
int lvalCD;
(
int k,lval2C 2D;
k=heir7(lval);
blanks!);
it((streq(line+lptr,"<")==0 )&
(streq(line+lptr*">" )= = 0H
(streq! 1 ine + lptr ,"<=") ==0H
(streq(line«-lptr, n >= n ) ==0))return k;
if (streq( line*lptr* M »"))return k;
if(streq(line*lptr/"<<" ))return k;
if(k)rvalue(lval);
while(l)
(if (match("<="))
(push!);
if(heir7(lval2))rvalue()val2);
pop();
if(cptr=lvalCOD)
if(cptrCidentD==pointer)
(ule();
continue;
>
if(cptr=lval2C01)
if(cptrCidentD==pointer)
(ule();
continue;
)
led;
)
else if (match(">="))
(push!);
if(heir7(1va12))rvalue!Ival2);
pop();
if(cptr=lvalC0D)
if(cptrCidentD==pointer)
(uge();
continue;
>
if(cptr=lval2C0D)
if(cptrCidentD==pointer)
(uge();
continue;
)
ge();
)
else if((streq(line*lptr, M <"))i
(streq(line*lptr,"«")== 0 ))
(inbyte();
push!);
if(heir7(lval2))rvalue!lval2);
popd;
if(cptr=lvalC0D)
lf(cptrCideotD==pointer)
(ult();
continue;
)
if(cptr=lval2C0D)
if(cptrCidentD==pointer)
(ult();
continue;
>
ltd;
>
else if((streq(l ine*lptr,">"))&
(streq(l ine+lptr / ,, » ,, )==0))
(inbyte!);
push();
If(heir7(lval2))rvalue(lval2);
popd;
if(cptr=lvalC0J)
if(cptrCidentD==pointer)
(ugt();
continue;
)
if(cptr=lval2C0D)
if(cptrCidentD==pointer)
(ugt();
continue;
)
gtd;
Number 45
186
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 15
else return 0;
)
>
/* >>»» start of ccb <«<« */
heir7(lval)
int lvdlCD;
C
int k,lval2C2D;
k=heir8(lval );
blanks( );
if ((streq(line+lptr / ">>")==OH
(streq(line+lptr,"<<")==0))return k;
if(k)rvalue(lval);
uhile(l)
(if (iratch( M >>") )
CpushO;
if(heir8(lval2))rvalue(lwal2);
pop();
asr();
)
else if (■atch( ,, « M >)
CpushO;
if(heir8(lval2))rvalue(lval2);
pop();
asl();
)
else return 0;
helc8(lval)
int lvalCD;
(
int k,lval2C21;
k=heir9(lval);
blanks();
lf((ch()! = '-fr'H(ch()l = '- 4
if(k)rvalue(lval);
whiled)
(if CwatchC'e"))
(push();
))return k;
if(heir9(lval2))rvalue(lval2);
if Ceptr=lvalCOD)
if((cptrCidentD==pointerH
(cptrCtype3==cint))
doublereq();
pop();
add();
)
else if (matchC
pop();
sub();
)
else return 0;
)
)
hell9(lval)
int lvalCi;
(
int k,lval2C21;
k=heir10(1val);
blanks();
if((ch()l= # *')4(ch()!='/ # )&
(ch()1='%'))return k;
if(k)rvalue(lval);
whlle(1)
(if (■atch("*"))
CpushO;
CpushO;
If(heir9(lval2))rvalue(lval2);
if (cptr=lvalC01)
if((cptrCidentl==pointer)C
(cptrC typel==cint))
doubleregO;
it(helr9(lval2))rvalue(lval2);
pop();
nult();
)
else if («atch("/"))
CpushO;
lf(helrlO(lval2))rvalueClval2);
pop();
divO;
)
else if (reatchCV*))
CpushO;
if(heirl0(1val2))rvalue(1val2);
PopO;
ood();
>
else return 0;
)
heii lO(lval)
int lvalCi;
int k;
char *ptr;
if (matchC***"))
Cif((k=helrl0(lval))==0)
Cneedlva1();
return 0;
>
if(IvalClD)pushC);
rvalue(lval);
inc();
ptr=lvalCO 3;
if((ptrCidentl==pointer)l
(ptrC typel==cint))
inc();
store(lval);
return 0;
>
else if(aatch("—"))
Cif((k=helrlO(lval))==0)
Cneedlva1( );
return 0;
)
if(lvalCll)push();
rvalue(lval);
dec();
ptr=lvalC0);
if((ptrCidentl==pointer)C
(ptrCtypel==cint))
dec();
store(lval);
return 0;
>
else if (raatchC*-"))
(k = heirl0(lval);
if (k) rvalue(lval);
neg();
return 0;
)
else if(matchC**"))
Ck = heir10(1 va 1);
if(k)rvalue(lval);
lvalCll=cint;
if(ptr=lvalC0D)lvalCll=ptrCtype3;
lvalC03=0;
return 1;
>
else if CmatchC’C"))
Ck=heirl0(lval);
if (k==0)
CerrorC"illegal address");
return 0;
)
else if ( lvalC IDreturn 0;
else
Cimmed();
outstr(ptr=lvalC03);
n 1 ();
lvalCll=ptrCtypel;
return 0;
)
tk=helrll(lval);
if(matchC))
Cit(k==0)
CneedlvalC);
return 0;
)
if(lvaltll)push();
r valued val);
inc();
P tr = lvalCOD;
if((ptrCidentl==polnter)l
(ptrCtypel==cint))
inc();
store(lval);
dec();
if((ptrCidentl==pointer)C
(ptrC typel==cint))
dec();
return 0;
)
else it(match("—"))
Cif(k==0)
CneedlvalC);
return 0;
3
if(lvalCll)push();
rvalueClval);
deed;
ptr=lvalCOD;
if((ptrCidentl==pointer)^
(p trC typeD==cint))
dec();
store(lval);
incO ;
if((ptrCident3 = =pointer H
(ptrCtypeD==cint))
inc();
return 0;
>
else return k;
)
>
/* >>»» start of cc7 <<«« V
heirlK lval)
int *1val;
C int k;char *ptr;
k=primary(lval);
ptr=lvalC0D?
blanks();
i f ((ch( )•== *C *) | (ch()=='( *))
whiled)
Page 16
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
187
(if(match("(") )
Ci f(ptr = = 0)
(errorC'can't subscript");
)unk();
needbrack!")");
return 0;
)
else if(ptr(ident3==pointer)rvalue(lval);
else if(ptrCident3l=array)
(error("can't subscript");
k=0;
)
push();
expression! );
needbrack!")");
if (ptretype)==cInt)doublereg();
pop();
add();
lval(03=0;
1valC13=ptretype);
k=l;
)
else if(ma tch("("))
(if(ptr==0)
(califunction(O);
)
else lf(ptr(ident)l=functlon)
(rvalue!1val);
calllunction(O);
)
else cal Ifunction(ptr);
k= 1 valCO 3 = 0;
>
else return k;
>
if(ptr==0)re turn k;
if(ptrtident3==function)
(immed!);
outstr(ptr);
nl();
return 0;
>
return k;
)
primary!lval)
int Mval;
( char *ptr,snametnanesize3;int numtl);
int k;
if(Eatch("("))
(k=helrl(lval);
needbrack!")");
return k;
>
if (symnatne(snane) )
(if(ptr=findloc(sname))
CgetlocCptr);
lvalt 03=ptr;
lvaltl3=ptr(type!;
lf(ptr(ident)==pointer)lval(13=cint;
i f(ptrtident)==array)return 0;
else return 1;
)
if(ptr=findglb(sname))
if(ptrCiden131=function)
(lval(03=ptr;
lvalt13=0;
if(ptrtident3!=array)return l;
iramed();
outstr(ptr);nl();
lvalt13=ptrCtype3;
return 0;
)
ptr = addglb(snarae# function,cint/0);
lvalt03=ptr;
lvaltl3=0;
return 0;
>
if(constant(nun))
re turn(1val(0 3 = 1val113 = 0);
else
(error("invalid expression");
imned();outdec(0);nl();
JunkO;
return 0;
>
)
store(lval)
int Mval;
( if ( lvaltl3==0)putineiL(lvait03);
else putstk(lvaltl3);
)
rvalue(lval)
int Mval;
( if((lvalto3 |= 0) & (lvaltl) == 0))
getraemO valt03);
else indirect(lval(l3);
)
test(label)
int label;
(
needbr ack("(");
expression();
needbtack(")")J
testJump(label);
)
constant(val)
int valt);
( if (number(val))
immed! );
else if (pstr(val))
immed!);
else if (qstr(val))
(iismed();printlabel(lltlab);outbyte(' + );)
else return 0 )
outdec(val(0 3);
nl();
return 1;
)
number(va1)
int valt);
( int k,minus;char c;
k=minus=l;
whlle(k)
(k=0;
if ( match("♦")) k=l;
if ( iratch( "-")) (minus=(-ninus);k = 1;>
>
if(nuraeric(ch())==0)return 0;
while (numeric(ch( )))
(c = inhyte( );
k=k*10+(c-'0');
)
if (rrlnus<0) k=(-k);
valt03=k;
return 1;
)
pstr(val)
int valt);
( int k;char c;
k = 0;
if (match("'")==0) return 0;
while((c=gch())1=39)
k=(k (255)*256 ♦ (cU27);
valt03=k;
return 1;
)*
qstr(val)
int vait3;
€ char c;
if (match(quote)==0) return 0;
valt03=litptr;
while (ch()!='"*)
(if(ch()==0)break;
if(1itpt r>=11tmax)
(error("string space exhausted");
while(reatch(quote)==0)
if(gch()==0)break;
return 1;
>
lltqtlltptr*+3=gch();
>
gch();
litqtlitptr**)=0;
return 1;
)
/* >>>>>> start of cc8 <<««< */
/* Begin a comment line for the assembler */
comment!)
( outbyte(';*);
)
/* Print all assembler info before any code is generated */
header!)
( comment!);
outstrC'smal1-c coopller rev 1.1");
nl();
>
/* Print any assembler stuff needed after all code */
trailer!)
( /* ol("EkD"); */
)
/* Fetch a static memory cell into the primary register */
ge tmem(sym)
char *sym;
( if((symtident3l=pointer)&!symttypel==cchar ) )
(ot("LDA ");
outstr(sya*name);
nl ();
call("ccsxt");
)
else
(ot("LHLD ");
outs tr(sy ra+name);
nl();
)
>
/* Fetch the address of the specified symbol */
/* into the primary register */
getloc(sym)
char *sym;
( immed();
outdec(((syra(offset)i255)+
((symtof f set* 135.255 )«8 ))-
3p)>
nl();
olC'DAD SP");
1
/* Store the primary register into the specified */
Number 45
188
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 17
/* static memory cell •/
putmera(sym)
char *sym;
( if((symCldentll=pointer)&(syroCtypeD==cchar))
(o1("MOV A,L" ) ;
otC'STA ");
)
else otC'SHLD ");
outstr(sym+name);
nl();
)
/* Store the specified object type in the primary register */
✓ * at the address on the top of the stack */
putstk(typeobj)
char typeobj;
( pop();
if(typeobj==cchar)ca11!"ccpchar");
else call("ccpint");
)
/* Fetch the specified object type indirect through the */
/* primary register into the primary register •/
indirect!typeobj)
char typeobj;
( if(typeobj==cchar)callC'ccgchar");
else cal 1("ccgint");
)
/* Swap the primary and secondary registers */
swap!)
C ol("XCHG");
)
/* Print partial Instruction to get an Immediate value */
/* into the primary register */
immed()
t otC'LXI H,");
)
/* Push the primary register onto the stack */
push!)
( o1("PUSH H");
} sp=sp-2;
/* Pop the top of the stack into the secondary register */
pop()
C o1!"POP D n );
sp=sp>2;
)
/• Swap the primary register and the top of the stack */
swapstk!)
t ol ("XTHL");
)
/* Call the specified subroutine name */
calUsname)
char *sname;
C o t("CA LL ");
outstr(sname);
nl!);
)
/* Return from subroutine */
ret!)
( ol!"PET");
)
/* Perform subroutine call to value on top of stack */
ca1lstk!)
( inured!);
outstr ! M s>5");
nl!);
swapstk!);
ol! "FCHL");
sp=sp*2;
)
/* Jump to specified internal label number */
jump! label)
int label;
( ot!"JHP ");
printlabe1!label ))
nl!);
)
/* Test the primary register and jump if false to label */
testjump!label)
int label;
C ol("KUV A,h");
o 1!"ORA L");
ot!"JZ ");
printlabelflabel);
nl!);
>
/* Print pseudo-op to define a byte */
de fbyte!)
( otf'DB ");
)
/•Print pseudo-op to define storage */
de fstorage!)
< ot!"DS ");
)
/• Print pseudo-op to define a word */
defwordf)
C ot!"OW ");
)
/* Modify the stack pointer to the new value indicated */
modstkinewsp)
int newsp;
( int k;
k=newsp-sp;
if!k==0)return newsp;
if(k>=0)
Cif!k<7)
Cif(kU)
Col!"IKX SP");
k—;
)
while(k)
(ol!"POP B");
k=k-2;
)
return newsp;
)
)
if!k<0)
Cif(k>-7)
(lt(kil)
(ol!"DCX SP M );
k++;
)
while(k)
(o 1 ("PUSH B");
k=k42;
)
swap!);
immed();outdec(k);nl();
olC'DAD SP");
o IC'SPHL");
swap!);
return newsp;
)
/• Double the primary register •/
doublereg()
( olC'DAD H");
>
/* Add the primary and secondary registers •/
/* (results in primary) •/
add!)
C o 1("DAD D");
)
/• Subtract the primary register from the secondary */
/* (results in primary) •/
sub! )
( callC'ccsub");
)
/• Hultiply the primary and secondary registers •/
/* (results in primary •/
mult!)
( callC'ccsult");
>
/* Divide the secondary register by the primary */
/* (quotient in primary, remainder in secondary) */
div!)
( cal1("ccdiv");
)
/• Compute remainder (mod) of secondary register divided •/
/* by the primary */
/* (remainder in primary, quotient in secondary) •/
mod( )
( div();
swap!);
>
/• Inclusive 'or* the primary and the secondary registers */
/* (results in primary) */
or!)
(call!"ccor");)
/• Exclusive 'or' the primary anc seconday registers •/
/* (results in primary) */
xor ( )
(call!"eexor");)
/* 'And' the primary and secondary registers */
/* (results in primary) •/
and! )
CcallC'ccand");) •
/* Arithmetic shift right the secondary register number of */
/* times in primary (results in primary) •/
asr( )
(cal 1!"ccasr");)
/• Arithmetic left shift the secondary register number ot */
/* times in primary (results in primary) */
as 1( )
CcallC'ccasl");)
/• Form two's complement of primary register •/
neg( )
(call!"ccneg");)
/• Form one's complement of primary register •/
com!)
(call!"cccora"); )
/* Increment the primary register by one •/
inc!)
ColC'INX H");>
/* Decrement the primary register by one •/
dec!)
(ol("DCX H");>
/• Following are the conditional operators */
/• They compare the secondary register against the primary •/
/• and put a literal 1 in the primary if the condition is */
/* true, otherwise they clear the primary register •/
/* Test for equal */
eq()
(call!"cceq");)
Page 18
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
189
/* Test lor not equal */
neC)
(call("ccne");)
/* Test lor less than (signed) */
lt()
Ccal 1("cclt");)
/* Test lor less than or equal to (signed) */
le()
(call("ccle");)
/• Test lor greater than (signed) */
gt()
(cal1("ccgt");)
/* Test for greater than or equal to (signed) */
ge()
(callC'ccge" )/ >
/* Test for less than (unsigned) */
ult()
(callO'ccult");)
/* Test lor less than or equal to (unsigned) »/
ule()
(cal1("ccule");)
/* Test lor greater than (unsigned) */
ugt()
(cal 1( "ccugt''); )
/* Test lor greater than or equal to (unsigned) */
uge( )
(cal1("ccuge");)
/* <<<<< End ol compiler »>» */
Number 45
190
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 19
UNIX Time-Sharing System- -
The C
Programming
Language
BY D. M. RITCHIE, S. C. JOHNSON,
M. IE. LESK, AND B. W. KERNIGHAN
Bell Laboratories
600 Mountain Avenue
Murray Hill, NJ 07974
C is a general-purpose programming
language that has proven useful for a
wide variety of applications. It is the
primary language of the UNIX* system,
and is also available in several other en¬
vironments. This paper provides an over¬
view of the syntax and semantics of C
and a discussion of its strengths and
weaknesses.
C is a general-purpose programming
language featuring economy of expres¬
sion, modem control flow and data
structure capabilities, and a rich set of
operators and data types.
C' is not a “very high-level” language
nor a big one and is not specialized to
any particular area of application. Its
generality and an absence of restrictions
make it more convenient and effective for
many tasks than supposedly more power¬
ful languages. C has been used for a wide
variety of programs, including the UNIX
operating system, the C compiler itself,
and essentially all UNIX applications
software. The language is sufficiently
expressive and efficient to have com¬
pletely displaced assembly language
programming on UNIX.
•UNIX is a trademark of Bell Laboratories.
© 1978, American Telephone and Telegraph
Company; Reprinted by permission.
C was originally written for the PDP-
11 under UNIX, but the language is not
tied to any particular hardware or operat¬
ing system. C compilers run on a wide
variety of machines, including the
Honeywell 6000, the IBM System/370,
and the Interdata 8/32.
I. THE LINGUISTIC HISTORY
OF C
The C language in use today 1 is the
product of several years of evolution.
Many of its most important ideas stem
from the considerably older, but still
quite vital, language BCPL 2 developed by
Martin Richards. The influence of BCPL
on C proceeded indirectly through the
language B, 3 which was written by Ken
Thompson in 1970 for the first UNIX
system on the PDP-11.
Although neither B nor C could really
be considered dialects of BCPL, both
share several characteristic features with
it:
(/) All are able to express the funda¬
mental flow-control constructions
required for well-structured pro¬
grams: statement grouping, deci¬
sion-making (if), looping (while)
with the termination test either at
the top or the bottom of the loop,
and branching out to a sequence of
possible cases (switch). It is inter¬
esting that BCPL provided these
constructions in 1967, well before
the current vogue for “structured
programming.”
(if) All three languages include the
concept of “pointer” and provide
the ability to do address arithmetic,
(iff) In all three languages, the argu¬
ments to functions are passed by
copying the value of the argument,
and it is impossible for the function
to change the actual argument.
When it is desired to achieve “call
by reference,” a pointer may be
passed explicitly, and the function
may change the object to which the
pointer points. Any function is
allowed to be recursive, and its
local variables are typically “auto¬
matic” or specific to each
invocation.
(z'v) All three languages are rather low-
level, in that they deal with the
same sorts of objects that most
computers do. BCPL and B restrict
their attention almost completely
to machine words, while C widens
its horizons somewhat to characters
and (possibly multi-word) integers
and floating-point numbers. None
deals directly with composite
objects such as character strings,
sets, lists, or arrays considered as a
whole. The languages themselves do
not define any storage allocation
facility beside static definition and
the stack discipline provided by the
local variables of functions; like¬
wise, I/O is not part of any of these
languages. All these higher mecha¬
nisms must be provided by explicit¬
ly called routines from libraries.
B and BCPL differ mainly in their syn¬
tax, and many differences stemmed from
the very small size of the first B compiler
(fewer than 4K 18-bit words on the PDP-
7). Several constructions in BCPL en¬
courage a compiler to maintain a repre¬
sentation of the entire program in mem¬
ory. In BCPL, for example,
valof $ (
resultis expression
$)
is syntactically an expression. It provides
a way of packaging a block of many
statements into a sort of unnamed inter¬
nal procedure yielding a single result
(delivered by the resultis statement). The
valof construction can occur in the mid¬
dle of any expression, and can be arbi¬
trarily large. The B language avoided the
difficulties caused by this and some other
Page ?0
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
191
constructions by rigorously simplifying
(and in some cases adjusting to personal
taste) the syntax of BCPL.
In spite of many syntactic changes, B
remained very close to BCPL seman¬
tically. The most characteristic feature of
both languages is their nearly identical
treatment of addresses (pointers). They
support a model of the storage of the
machine consisting of a sequence of
equal-sized cells, into which values can be
placed; in typical implementations, these
cells will be machine words. Each identi¬
fier in a program corresponds to a cell,
and a cell may contain a variety of values.
Most often the value is an integer, or
perhaps a respresentation of a character.
All the cells, however, are numbered; the
address of a cell is just the integer giving
its ordinal position. BCPL has a unary
operator lv (in some versions, and also in
B and C, shortened to &) that, when ap¬
plied to a name, yields the address of the
cell corresponding to the name. The in¬
verse operator rv (later *) yields the value
in the cell pointed to its argument. Thus
the statement
px = &x;
of B assigns to px the number that can be
interpreted as the address of x; the
statements
y = *px + 2;
*px = 5;
first use the value in the cell pointed to
by px (which is the same cell as x) and
then assign 5 to this cell.
Arrays in BCPL and B are intimately
tied up with pointers. An array declara¬
tion, which might in BCPL be written
let Array = vec 10
and in B
auto Array [10];
creates a single cell named Array and
initializes it with the address of the first
of a sequence of 10 unnamed cells
containing the array itself. Since the
quantity stored in Array is just the
address of the cell of the first element
of the array, the expression
Array + i
is the address of the ith element, counting
from zero, likewise, applying the in¬
direction operator,
* (Array + i)
refers to the value of the ith member
of the array. This operation is so frequent
that special syntax was invented to
express it:
Array [i]
Thus, despite its asymmetric appear¬
ance, subscripting is a commutative
operation; the above example could
equally well be written
i [Array]
In BCPL and B there is only one type
of object, the machine word, so when
the same language operator is applied to
two operands, the calculation actually
carried out must always be the same.
Thus, for example, if one wishes to pro¬
vide the ability to do floating-point
arithmetic, the “+” operator notation
cannot be used, since it implies an integer
addition. Instead (in a version of BCPL
for the GE 635), a was placed in
front of each operator that had floating¬
point operands. As may be appreciated,
this was a frequent source of errors.
The machine model implied by the
definitions of BCPL and B is simple
and self-consistent. It is, however, in¬
adequate for many purposes, and on
many machines it causes inefficiencies
when implemented. The problems be¬
came evident to us after B began to be
used heavily on the first PDP-11 version
of UNIX. The first followed from the fact
that the PDP-11, like a number of mach¬
ines (including, for example, the IBM
System/370), is byte addressed; a
machine address refers to any of several
bytes (characters) in a word, not the word
alone. Most obviously, the word orienta¬
tion of B cut us off from any convenient
ability to access individual bytes. Equally
important was the fact that, before any
address could be used, it had to be shift¬
ed left by one place. The reason for
this is simple: there are two byte per
PDP-11 word. On the one hand, the
language guranteed that if 1 was added to
an address quantity, it would point to the
next word; on the other, the machine
architecture required that word addresses
be even and equal to the byte number
of the first byte in the word. Since,
finally, there was no way to distinguish
cells containing ordinary integers from
those containing pointers, the only solu¬
tion visible was to represent pointers
as word numbers and then, at the point
of use, convert to the byte representation
by multiplication by 2.
Yet another problem was introduced
by the desire to provide for floating¬
point arithmetic. The PDP-11 supports
two floating-point formats, one of which
requires two words, the other four.
In neither case was it satisfactory to use
the trick used on the GE 635 (operator
like “ .+ ”) because there was no way to
represent the requirement for a single
data item occupying four or eight bytes.
This problem did not arise on the 635
because integers and single-precision
floating-point both require only one
word.
Thus the problems evidenced by B
led us to design a new language that
(after a brief period under the name NB)
was dubbed C. The major advance pro¬
vided by C is its typing structure, which
completely solved the difficulties men¬
tioned above. Each declaration in a C
program specifies (sometimes implicitly)
a type, which determines how much stor¬
age the object requires and how it is to be
interpreted. The original fundamental
types provided were single character
(byte), integer, single-precision floating¬
point, and double-precision floating¬
point. (Others discussed below were
added later.) Thus in the program
double a,b;
a = b + 3;
the compiler is able to determine from
the declarations of a and b the fact that
they require four words of storage each,
that the “ + ” means a double-precision
floating add, and that “3 ” must be con¬
verted to floating.
Of course, the idea of typing variables
is in no way original with C; in fact,
it was the general rule among the most
widely used and influential languages,
including ALGOL, FORTRAN, and PL/I.
Nevertheless, the introduction of types
marked an important change in our own
thinking. The typeless nature of BCPL
and B had seemed to promise a great
simplification in the implementation,
understanding, and use of these lan¬
guages. By the time that C was created
(circa 1972), advocates of languages like
ALGOL 68 and PASCAL recommended a
strongly enforced type structure on
psychological grounds; but even dis¬
regarding their arguments, the typeless
nature of BCPL and B seemed inap¬
propriate, for purely technological
reasons, to be available hardware.
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n. THE TYPE STRUCTURE OF C
The introduction of types in C, al¬
though a major departure from the tra¬
dition of BCPL and B, was done in such
a way that many of the characteristic
usages of the earlier languages survived.
To some extent, this continuity was an
attempt to preserve as much as possible
of the considerable corpus of exisitng
software written in B, but even more
important, especially in retrospect, was
the desire to minimize the intellectual
distance beween the past and the future
ways of expression.
• (Array + i)
is the ith member itself, and
Array [i]
is another notation for the same thing.
In all these cases, of course, should
Array be an array of, or pointer to,
some objects other than integers, the
scale factor is adjusted appropriately.
The pointer arithmetic, as written, is
independent of the type of object to
which the pointer points and indeed of
the internal representation of the pointer.
2.2 Derived types
defines a template, called tag, for a
structure containing three members', an
integer i, a floating point number /,
and a three-character array c. The de¬
claration
struct tag x, y [10], *p;
declares a structure x of this type, an
array y of 10 such structures, and a point¬
er p to this kind of structure. The hier¬
archical nature of derived types is clearly
evident here: y is an array of structures
whose members include an array of
characters. References to individual
members of structures use the . operator.
x.i
x.f
y[i] -c[o]
(*p) • c[l]
Parentheses in the last line are necessary
because the.binds more tightly than*.
It turns out that pointers to structures
are so common that special syntax
is called for to express structure access
through a point.
P—>c[l]
P~>i
This soon becomes more natural than the
equivalent
(*p) ,c[l]
(*P) • i
A union is capable of holding, at
different times, objects of different
types, with the compiler keeping track
of size and alignment requirements.
Unions provide a way to manipulate
different kinds of data in a single part
of storage, without embedding machine-
dependent information (like the relative
sizes of int and float) in a program.
For example, the union u, declared
union {
int i;
float f;
}u;
can hold either an int (written ui) or
a float (written u.f.). Regardless of the
machine it is compiled on, it will be large
enough to hold either one of these
quantitites. A union is syntactically
identical to a structure; it may be con¬
sidered as a structure in which all the
members begin at the same offset.
2.1 Pointers, arrays and address
arithmetic
One clear example of the similarity of
C to the earlier languages is its treatment
of pointers and arrays. In C an array of
10 integers might be declared
int Array [10];
which is identical to the corresponding
declaration in B. (Arrays begin at zero;
the elements of Array are Array[0 ],
..., Arrayf 9] . As discussed above, the
B implementation caused a cell named
Array to be allocated and initialized with
a pointer to 10 otherwise unnamed cells
to hold the array. In C, the effect is
bit different; 10 integers are allocated,
and the first is associated with the name
Array. But C also includes a general rule
that, whenever the name of an array
appears, in an expression, it is converted
to a pointer to the first member of the
array. Strictly speaking, we should say,
for this example, it is converted to an
integer pointer since all C pointers are
associated with a particular type to which
they point. In most usages, the actual
effects of the slightly different meanings
of Array are indistinguishable. Thus in
tlie C expression
Array + i
The identifier Array is converted to a
pointer to the first element of the array;
i is scaled ( if required) before it is added
to the pointer. For a byte-addressed
machine, the scale factor is the number of
bytes in an integer; for a word-addressed
machine the scale factor is unity. In any
event, the result is a pointer to the ith
member of the array. Likewise identical
in. effect to the interpretation of B,
As mentioned above, the basic types
in C were originally int, which represents
an integer in the basic size provided by
the machine architecture; char , which
represents a single byte; float, a single-
precision floating-point number; and
double, double-precision floating-point.
Over the years, long, short, and unsigned
integers have been added. In current C
implementations, long is at least 32
bits; short is usually 16 bits; and int
remains the “natural” size for the
machine at hand. Unsigned integers
exist mainly to squeeze an extra bit out
of the machine, since the sign bit need
not be represented.
In addition to these basic types, C
provides a conceptually infinite her-
archy of derived types, which are formed
by composition of the basic types with
pointers, arrays, structures, unions, and
functions. Examples of pointer and array
declarations have already been exhibited;
another is
double *vecp, vector[100];
which declares a pointer veep to double-
precision floating numbers, and an array
vector of the same kind of objects. The
size of an array, when specified, must
always be a constant.
A structure is an aggregate of one or
more objects, usually of various types,
which can be treated as a unit. C struc¬
tures are essentially the same as records
in languages like PASCAL, and semanti¬
cally, though not syntactically, like PL/I
and Cobol structures. Thus,
struct tag {
int i;
float f;
char c[3];
>;
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Number 45
193
Unions in C are more analogous to PL/I’s
CALL than to the unions of ALGOL 68
or the variant records of PASCAL, be¬
cause it is the responsibility of the pro¬
grammer to avoid referring to a union
that does not currently contain an ob¬
ject of the implied type.
A function is a subprogram that
returns an object of a given type:
unsigned unsf();
declares a function that returns unsigned.
The type of a function ignores the
number and types of its arguments,
although in general the call and the de¬
finition must agree.
2.3 Type composition
The syntax of declarations borrows
from that of expressions. The key idea
is that a declaration, say
int ... ;
contains a part “ ... ” that, if it appeared
in an expression would be of type int.
The constructions seen so far, for ex¬
ample ,
int *lptr;
int lfunc();
int iarr [10];
exhibit this approach, but more compli¬
cated declarations are common. For
example,
int *funcptr();
int (*ptrfunc)();
declare respectively a function that
returns a pointer to an integer, and a
pointer to a function that returns an
integer. The extra parentheses in the
second are needed to make the * apply
directly to ptrfunc, since the implicit
function-call operator () binds more
tightly than *. Functions are not varia¬
bles, so array or structures of functions
are not permitted. However, a pointer to
a function, like ptrfunc, may be stored,
copied, passed as an argument, returned
by a function, and so on, just as any
other pointer.
Arrays of pointers are frequently used
instead of multi-dimensional arrays. The
usage of a and b when declared
int a[10] [10];
int *b [10];
may be similar, in that a [5] [5] and
b [5] [5] are both legal references to a
single int, but a is a true array: all 100
storage cells have been allocated, and
the conventional rectangular subscript
calculation is done. For b, however,
the declaration has only allocated 10
pointers; each must be set to point to an
array of integers. Assuming each does
point to a 10-element array, then there
will be 100 storage cells set aside, plus the
10 cells for the pointers. Thus the array
of pointers uses slightly more space and
may require an extra initialization step,
but has two advantages: it trades an
indirection for a subscript multiplication,
and it permits the rows of the array to be
of different lengths. (That is, each ele¬
ment of b need not point to a 10-
element vector; some may point to 2
elements, some to 20). Particularly with
strings whose length is not known in
advance, an array of pointers is often
used instead of a multidimensional array.
Every C main program gets access to its
invoking command line in this form, for
example.
The idea of specifying types by ap¬
propriating some of the syntax of
expressions seems to be original with C,
and for the simpler cases, it works well.
Occasionally some rather ornate types are
needed, and the declaration may be a bit
hard to interpret. For example, a pointer
to an array of pointers to functions, each
returning an int, would be written
int (*(*funnyarray)[])();
which is certainly opaque, although
understandable enough if read from the
inside out. In an expression, funnayarray
might appear as
i = (*(*funnyarray)[j] )(k);
The corresponding Algol 68 declaration is
ref [] ref proc int funny array
which read from left to right in corre¬
spondence with the informal description
of the type if ref is taken to be the equiv¬
alent of C’s “pointer to.” The Algol may
be clearer, but both are hard to grasp.
III. STATEMENTS AND
CONTROL FLOW
Control flow in C differs from other
languages primarily in details of syntax.
As in PL/1, semicolons are used to
terminate statements, not to separate
them. Most statements are just expres¬
sions followed by a semicolon; since
assignments are expressions, there is no
need for a special assignment statement.
Statements are grouped with braces {
and } , rather than with words like begin -
end or do-od, because the more concise
form seems much easier to read and is
certainly easier to type. A sequence of
statements enclosed in { } is syntac¬
tically a single statement.
The if-else statement has the form
if ( expression )
statement
else
statement
The expression is evaluated; if it is “true”
(that is, if expression has a non-zero
value), the first statement is done. If it is
“false” ( expression is zero) and if there is
an else part, the second statement is
executed instead. The else part is option¬
al; if it is omitted in a sequence of nested
iFs, the resulting ambiguity is resolved in
the usual way by associating the else with
the nearest previous else-less if.
The switch statement provides a multi¬
way branch depending on the value of an
integer expression:
switch ( expression )
case const:
code
case const :
code
default:
^ code
The expression is evaluated and compared
against the various cases, which are la¬
beled with distinct integer constant
values. If any case matches, execution
begins at that point. If no case matches
but there is a default statement, execu¬
tion begins there: otherwise, no part of
the switch is executed.
The cases are just labels, and so con¬
trol may flow through one case to the
next. Although this permits multiple
lables on cases, it also means that in gen¬
eral most cases must be terminated with
an explicit exit from the switch (the
break statement below).
The switch construction is part of C’s
legacy from BCPL; it is so useful and so
easy to provide that the lack of a
corresponding facility of acceptable
generality in languages ranging from For-
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Page 23
tran through Algol 68, and even to Pascal
(which does not provide for a default),
must be considered a real failure of
imagination in language designers.
C provides three kinds of loops. The
while is simply
while ( expression )
statement
The expression is evaluated; if it is true
(non-zero), the statement is executed,
and then the process repeats. When
expression becomes false (zero), execu¬
tion terminates.
The do statement is a test-at-the-
bottom loop:
do
statement
while ( expression );
statement is performed once, then ex¬
pression is evaluated. If it is true, the loop
is repeated; otherwise it is terminated.
The for loop is reminiscent of similar¬
ly named loops in other languaged, but
rather more general. The for statement
for (exprl ; expr2 ; expr3)
statement
is equivalent to
exprl ;
while (exprl)
statement
expr3 ;
}
Grammatically, the three components of
a for loop are expressions. Any of the
three parts can be omitted, although the
semicolons must remain. If exprl or
expr3 is left out, it is simply dropped
from the expansion. If the test, expr2, is
not present, it is taken as permanently
true, so
for (;;)
is an “infinite” loop, to be broken by
other means, for example by break,
below.
The for statement keeps the loop
control components together and visible
at the top of the loop, as in the idiomatic
for (i = 0; i < N;i = i+1)
which processes the first N elements of an
array, the analogue of the Fortran or
PL/1 DO loop. The for is more general,
however. The test is re-evaluated on each
pass through the loop, ana there is no
restriction on changing the variables
involved in any of the expressions in the
for statement. The controlling variable
i retains it value regardless of how the
loop terminates. And since the compo¬
nents of a for are arbitrary expressions,
for loops are not restricted to arithmetic
progressions. For example, the classic
walk along a linked list is
for (p = top; p != NULL; p = p - > next)
There are two statements for control¬
ling loops. The break statement, as men¬
tioned, causes an immediate exit from the
immediately enclosing while, for, do or
switch. The continue statement causes
the next iteration of the immediately
enclosing loop to begin, break and con¬
tinue are asymmetric, since continue does
not apply to switch.
Finally, C provides the oft-maligned
goto statement. Empirically, goto’s are
not much used, at least on our system.
The operating system itself, for example,
contains 98 in some 8300 lines. The PDP-
11 C compiler, in 9660 lines, has 147.
Essentially all of these implement some
form of branch to the top or bottom of
a loop, or to error recovery code.
IV. OPERATORS AND
EXPRESSIONS
C has been characterized as having a
relatively rich set of operators. Some of
these are quite conventional. For
example, the basic binary arithmetic
operators are +, -, * and /. To these, C
adds the modulus operator %: m%n is the
remainder when m is divided by n.
Besides the basic logical or bitwise
operators & (bitwise AND), and I (bit¬
wise OR), there are also the binary
operators A (bitwise exclusive OR),
>> (right shift), and << (left shift),
and the unary operator — (ones comple¬
ment). These operators apply to all inte¬
gers; C provides no special bit-string type.
The relational operators are the usual
>, > = , <, <=, == (equality test), and
!= (inequality test). They have the value
1 if the stated relation is true, 0 if not.
The unary pointer operators * (for
indirection) and & (for taking the ad¬
dress) were described in Section 1. When
y is such as to make the expressions
&*y or &*y legal, either is just equal to
y. Note that & and * are used as both
binary and unary operators (with dif¬
ferent meanings).
The simplest assignment is written =,
and is used conventionally: the value of
the expression on the right is stored in
the object whose address is on the left.
In addition, most binary operators can be
combined with assignment by writing
a op= b
which has the effect of
a = a op b
except that a is only evaluated once. For
example,
x += 3
is the same as
x = x + 3
if x is just a variable, but
p[i+j + 1] + = 3
adds 3 to the element selected from the
array p, calculating the subscript only
once, and, more importantly, requiring it
to be written out only once. Compound
assignment operators also seem to cor¬
respond well to the way we think; “add 3
to x” is said, if not written, much more
commonly than “assign x + 3 to x.”
Assignment expressions have a value,
just like other expressions, and may be
used in larger expressions. For example,
the multiple assignment
i = j = k = 0;
is a byproduct of this fact, not a special
case. Another very common instance is
the nesting of an assignment in the
condition part of an if or a loop, as in
while (c = getchar()) != EOF) ...
which fetches a character with the func¬
tion getchar, assigns it to c, then tests
whether the result is an end of file mark¬
er. (Parentheses are needed because the
precedence of the assignment = is lower
than that of the relational !=.)
C provides two novel operators for
incrementing and decrementing variables.
The increment operator + + adds 1 to its
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Number 45
195
operand; the decrement operator --
subtracts 1. Thus the statement
+ + i;
increments i. The unusual aspect is that
+ + and -- may be used either as prefix
operators (before the variable, as in + + i),
or postfix (after the variable i + +). In
both cases, the effect is to increment i.
But the expression + + i increments i
before using its value, while i + + incre¬
ments i after its value has been used. If
i is 5, then
x = i + +;
sets x to 5, but
x = + + i;
sets x to 6. In both cases, i becomes 6.
For example,
stack[i + +] = ... ;
pushes a value on a stack stored in an
array stack indexed by i, while
... = stack[--i];
retrieves the value and pops the stack. Of
course, when the quantity incremented
or decremented is a pointer, appropriate
scaling is done, just as if the “1” were
added explicitly:
*stackp + + =...;
... = *--stackp;
are analogous to the previous example,
this time using a stack pointer instead of
an index.
Tests may be combined with the log¬
ical connectives && (AND), || (OR), and
! (truth value negation). The && and ||
guarantee left-to-right evaluation, with
termination as soon as the truth value is
known. For example,in the test
if (i < = N && array [i] >0 ...
if i is greater than N, then array [i]
(presumably at that point an out-of-
bounds reference) will not be accessed.
This predictable behavior is especially
convenient, and much preferable to the
explicitly random order of evaluation
promised by most other languages. Most
C programs rely heavily on the properties
of && and ||.
Finally, the conditional expression,
written with the ternary operator ?:,
provides an analogue of if -else in expres¬
sions. In the expression
el ? e2 : e3
the expression el is evaluated first. If it is
non-zero (true), then the expression e2
is evaluated, and that is the value of the
conditional expression. Otherwise, e3 is
evaluated, and that is the value. Only one
of e2 and e3 is evaluated. Thus to set
z to the maximum of a and b,
z = (a > b) ? a : b;/* z = max(a, b) */
We have already discussed how inte¬
gers are scaled appropriately in pointer
arithmetic. C does a number of other
automatic conversions between data
types, more freely than Pascal, for
example, but without the wild abandon
of PL/1. In all contexts, char variables
and constants are promoted to int. This is
particularly handy in code like
n = c - ‘O’;
which assigns to n the integer value of the
character stored in c, by subtracting the
value of the character *0’. Generally, in
fact, the basic types fall into only two
classes, integral and floating-point; char
variables, and the various lengths of int’s,
are taken to be representations of the
same kind of thing. They occupy differ¬
ent amounts of storage but are essentially
compatible. Boolean values as such do
not exist; relational or truth-value expres¬
sions have value 1 if true, and 0 if false.
Variables of type int are converted to
floating-point when combined with floats
or doubles and in fact all floating arith¬
metic is carried out in double precision,
so floats are widened to double in
expressions.
Conversions that involve “narrowing”
an expression (for example, when a
longer value is assigned to a shorter) are
also well behaved. Floating point values
are converted to integer by truncation;
integers convert to shorter integers or
characters by dropping high-order bits.
When a conversion is desired, but is
not implicit in the context, it is possible
to force a conversion by an explicit
operator called a cast. The expression
{type) expression
is a new expression whose type is that
specified in type, for example, the sin
routine expects an argument of type
double; in the statement
x = sin((double) n);
the value of n is converted to double
before being passed to sin.
V. THE STRUCTURE OF
C PROGRAMS
Complete programs consist of one
or more files containing function and
data declarations. Thus, syntactically, a
program is made up of a sequence of
declarations; executable code appears
inside functions. Conventionally, the run¬
time system arranges to call a function
named main to start execution.
The language distinguishes the notions
of declaration and definition. A decla¬
ration merely announces the properties
of a variable (like its type); a definition
declares a variable and also allocates
storage for it or, in the case of a function,
supplies the code.
5.1 Functions
The notion of function in C includes
the subroutines and functions of FOR¬
TRAN and the procedures of most other
languages. A function call is written
namefarglist)
where the parentheses are required even
if the argument fist is empty. All func¬
tions may be used recursively.
Arguments are passed by value, so
the called function cannot in any way
affect the actual argument with which it
was called. This permits the called pro¬
gram to use its formal arguments as
conveniently initialized local variables.
Call by value also eliminates the class
of errors, familiar to FORTRAN pro¬
grammers, in which a constant is passed
to a subroutine that tries to alter the
corresponding argument. An array name
as an actual argument, however, is con¬
verted to a pointer to the first array
element (as it always is), so the effect
is as if arrays were called by reference;
given the pointer, the called function
can work its will on the individual
elements of the array. When a function
must return a value through its argument
list, an explicit pointer may be passed,
and the function referencec the ultimata
target through this pointer. For example,
the function swapfpa, pb) interchanges
two integers pointed to by its arguments:
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swap(px, py) /* flip int’s
pointed to by px
and py */•
int *px, *py;
int temp;
{
temp = *px;
*px = *py;
*py = temp;
}
This also demonstrates the form of
a function definition: the name is fol¬
lowed by an argument list; the arguments
are declared, and the body of the func¬
tion is a block, or compound statement,
enclosed in braces. Declarations of local
variables may follow the opening brace.
A function returns a value by
return expression ;
The expresssion is automatically coerced
to the type that the function returns.
By default, functions are assumed to re¬
turn int; if this is not the case, the func¬
tion must be declared both in the cal¬
ling routine and when it is defined.
For example, a function definition is
double sqrt(x) /* returns square root
of x */
double x;
{
}
In the caller, the declaration is
double y, sqrt();
«
y = sqrt(y);
A function argument may be any of
the basic types or a pointer, but not an
array, structure, union, or function.
The same is true of the value returned
by a function, (the most recent versions
of the language, still not standard every¬
where, permit structures and unions as
arguments and values of functions and
allow them to be assigned.)
5.2 Data
Data declared at the top level (that is,
outside the body of any function defi¬
nition) are static in lifetime, and exist
throughout the execution of the pro¬
gram. Variables declared within a func¬
tion body are by default automatic-.
they come into existence when the func¬
tion is entered and vanish when it is
exited. Automatic variables may be
declared to be register variables; when
possible they will be placed in machine
registers, which may result in smaller,
faster code. The register declaration
is only considered a hint to the compiler;
no hardware register names are men¬
tioned, and the hint may be ignored if
the compiler wishes.
Static variables exist throughout the
execution of a program, and retain their
values across function calls. Static vari¬
ables may be local to a function or (if
defined at the top level) common to
several functions.
External variables have the same life¬
time as static, but they are also accessible
to programs from other source files. That
is, all references to an identically named
external variable are references to the
same thing.
The “storage class” of a variable can
be explicitly announced in its
declaration:
static int x;
extern double y [ 10];
More often the defaults for the context
are sufficient. Inside a function, the
default is auto (for automatic). Outside
a function, at the top level, the default
is extern. Since automatic and register
variables are specific to a particular call
of a particular function, they cannot be
declared at the top level. Neither top-
level variables nor functions explicitly
declared static are visible to functions
outside the file in which they appear.
5.3 Scope
Declarations may appear either at the
top level or at the head of a block
(compound statement). Declarations in
an inner block temporarily override those
of identically named variables outside.
The scope of a declaration persists until
the end of its block, or until the end of
the file, if it was at the top level.
Since function definitions may be
given only at the top level (that is, they
may not be nested), there are no internal
procedures. They have been forbidden
not for any philosophical reason, but
only to simplify the implementation. It
has turned out that the ability to make
certain functions and data invisible to
programs in other files (by explicitly
declaring them static) is sufficient to
provide one of their most important
uses, namely hiding their names from
other functions. (However, it is not
possible for one function to access the
internal variables of another, as internal
procedures could do.) Similarly, the
ability to conceal functions and data in
one file from access by another satisfies
some of the most crucial requirements of
modular programming (as in languages
like Alphard, CLU, and Euclid), even
through it does not satisfy them all.
VI. C PREPROCESSOR
It is well recognized the “magic num¬
bers” in a program are a sign of bad
programming. Most languages, therefore,
provide a way to define symbolic names
for constants, so that the value of a magic
number need be specified in only one
place, and the rest of the code can refer
to the value by some mnemonic name.
In C such a mechanism is available, but
it is not part of the syntax of the
language; instead, symbolic naming is
provided by a macro preprocessor auto¬
matically invoked as part of every C
compilation. For example, given the
definitions
# define PI 3.14159
#define E 2.71284
the preprocessor replaces all occurrences
of a defined name by the corresponding
defining string. (Upper-case names are
normally chosen to emphasize that these
are not variables.) Thus, when the pro¬
grammer recognizes that he has written
an incorrect value for e, only the defini¬
tion line has to be changed to
# define E 2.71828
instead of each instance of the constant
in the program.
Providing this service by a macro
processor instead of by syntax has some
significant advantages. The replacement
text is not restricted to being numbers;
any string of characters is permitted.
Furthermore, the token being replaced
need not be a variable, although it must
have the form of a name. For example,
one can define
# define forever for(;;)
and then writen infinite loops as
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Number 45
197
forever {
}
The macro processor also permits
macros to have arguments; this capability
is heavily used by some I/O packages.
A second service of the C preprocessor
is library file include: a source line of
the form
#include “name”
causes the contents of the file name to be
interpolated into the source at that
point, (includes may be nested.) This
feature is much used, especially in
larger programs, for making sure that
all the source files of the program are
supplied with identical # defines, global
data declarations, and the like.
VII. ENVIRONMENTAL
CONSIDERATIONS
By intent, the C language confines
itself to facilities that can be mapped
relatively efficiently and directly into
machine instructions. For example,
writing matrix operations that look ex¬
actly like scalar operations is possible in
some programming languages and
occasionally misleads programmers into
believing that matrix operations are
as cheap as scalar operations. More
important, restricting the domain of the
C compiler to those areas where it knows
how to do a relatively efficient job
provides the freedom to design sub¬
routine libraries for the remaining tasks
without constraining them to fit into
some language specification. When the
compiler cannot implement some facility
without heavy costs in nonportability,
complexity, or efficiency, there are many
benefits to leaving out such a facility: it
simplifies the language and the compiler,
frequently without inconveniencing the
user (who often rejects a high-cost
built-in operation and does it himself
anyway).
At present, C is restricted to simple
operations on simple data types. As a
result, although the C area of operation
is comparatively clean and pleasant, the
user must know something about the
polluting effects of the environment to
get most jobs done. A program can
always access the raw system calls on
each system if very close interaction with
the operating system is needed, but
standard library routines have been imple¬
mented in each C environment that try to
encourage portability while retaining
speed and flexibility. The basic areas
covered by the standard library at present
are storage allocation, string handling,
and I/O. Additional libraries and utilities
are available for such areas as graphics,
coroutine sequencing, execution time
monitoring, and parsing.
The only automatic storage manage¬
ment service provided by C itself is the
stack discipline for automatic variables.
Two subroutines exist for more flexible
storage handling. The function
calloc(n,s) returns a pointer to a
properly aligned storage block that will
hold n items each of which is s bytes
long. Normally s is obtained from the
sizeof pseudo-function, a compile-time
function that yields the size in bytes of a
variable or data type. To return a block
obtained from calloc to the free storage
pool, cfree(p) may be called, where p is
a value returned by a previous call to
calloc.
Another set of routines deals with
string handling. There is no “string” data
type, but an array of characters, with a
convention that the end of a string is
indicated by a null byte, can be used for
the same purpose. The most commonly
used string routines perform the func¬
tions of copying one string to another,
comparing two strings, and computing
a string length. More sophisticated string
operations can often be performed using
the I/O routines, which are described
next.
Most of the routines in the standard
library deal with input and output. Most
C programmers use stream I/O, although
there is no reason why record I/O could
not be used with the language. There are
three default streams: the standard input,
the standard output, and the error
output. The most elementary routines for
dealing with these streams are getchar()
which reads a character from the standard
input, and putchar(c), which writes the
character c on the standard output. In the
environments in which C programs run, it
is generally possible to redirect these
streams to files or other programs; the
program itself does not change and is
unaware of the redirection.
The most common output function is
printf(format, datal, data2,...), which
performs data conversion for formatted
output. The string format is copied to the
standard output, except that when a
conversion specification introduced by a
% character is found in format it is
replaced by the value of the next data
argument, converted according to the
specification. For example,
printf (”n = %d, x = %f”, n, x);
prints n as a decimal integer and x as a
floating point number, as in
n = 17, x = 12.34
A similar function scanf performs for¬
matted input conversion.
All the routines mentioned have
versions that operate on streams other
than the standard input or output, and
printf and scanf variants may also process
a string, to allow for in-memory format
conversion. Other routines in the I/O
library transmit whole lines between
memory and files, and check for error or
end-of-file status.
Many other routines and utilities are
used with C, somewhat more on UNIX
than on other systems. As an example,
it is possible to compile and load a C
program so that when the program is run,
data are collected on the number of times
each function is called and how long it
executes. This profile pinpoints the
parts of the program that dominate the
run-time.
VIII. EXPERIENCE WITH C
C compilers exist for the most widely
used machines at Bell Laboratories (the
IBM S/370, Honeywell 6000, PDP-11)
and perhaps 10 others. Several hundred
programmers within Bell Laboratories
and many outside use C as their primary
programming language.
8.1 Favorable experiences
C has completely displaced assembly
language in UNIX programs. All applica¬
tions code, the C compiler itself, and the
operating system (except for about 1000
lines of initial bootstrap, etc.) are written
in C. Although compilers or interpreters
are available under UNIX for Fortran,
Pascal, Algol 68, Snobol, APL, and other
languages, most programmers make little
use of them. Since C is a relatively low-
level language, it is adequately efficient
to prevent people from resorting to
assembler, and yet sufficiently terse and
expressive that its users prefer it to PL/1
or other very large languages.
A language that doesn’t have every¬
thing is actually easier to program in than
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Page 27
some that do. The limitations of C often
imply shorter manuals and easier training
and adaptation. Language design, espe¬
cially when done by a committee, often
tends toward including all doubtful
features, since there is no quick answer to
the advocate who insists that the new
feature will be useful to some and can be
ign ored by others. But this results in long
manuals and hierarchies of “experts” who
know progressively larger subsets of the
language. In practice, if a feature is not
used often enough to be familiar and does
not complete some structure of syntax or
semantics, it should probably be left out.
Otherwise, the manual and compiler get
bulky, the users get surprises, and it
becomes harder and harder to maintain
and use the language. It is also desirable
to avoid language features that cannot be
compiled efficiently; programmers like to
feel that the cost of a statement is com¬
parable to the difficulty in writing it. C
has thus avoided implementing operations
in the language that would have to be
performed by subroutine call. As com¬
piler technology improves, some exten¬
sions (e.g., structure assignment) are
being made to C, but always with some
principles in mind.
One direction for possible expansion
of the language has been explicitly
avoided. Although C is much used for
writing operating systems and associated
software, there are no facilities for multi¬
programming, parallel operations, syn¬
chronization, or process control. We
believe that making these operations
primitives of the language is inappro¬
priate, mostly because language design is
hard enough in itself without incorpo¬
rating into it the design of operating
systems. Language facilities of this sort
tend to make strong assumptions about
the underlying operating system that may
match very poorly what it actually does.
8.2 Unfavorable experiences
The design and implementation of C
can (or could) be criticized on a number
of points. Here we discuss some of the
more vulnerable aspects of the language.
8.2.1 Language level
Some users complain that C is an
insufficiently high-level language; for
example, they want string data types and
operations, or variable-size multi-dimen¬
sional arrays, or generic functions. Some¬
times a suggested extension merely
involves lifting some restriction. For
example, allowing variable-size arrays
would actually simplify the language
specification, since it would only involve
allowing general expressions in place of
constants in certain contexts.
Many other extensions are plausible;
since the low level of C was praised in the
previous section as an advantage of the
language, most will not be further
discussed. One is worthy of mention,
however. The C language provides no
facility for I/O, leaving this job to
library routines. The following fragment
illustrates one difficulty with this
approach:
printf(”%d\n”, x);
The problem arises because on machines
on which int is not the same as long, x
may not be long; if it were, the program
must be written
printf(”%D\n”,x);
so as to tell printf the length of x. Thus,
changing the type of x involves changing
not only its declaration, but also other
parts of the program. If I/O were built
into the language, the association
between the type of an expression and
the format in which it is printed could
be reconciled by the compiler.
8.2.2 Type safety
C has traditionally been permissive in
checking whether an expression is used in
a context appropriate to its type. A
complete fist of examples would be long,
but two of the most important should
illustrate sufficiently. The types of formal
arguments of functions are in general not
known, and in any case are not checked
by the compiler against the actual argu¬
ments at each call. Thus in the statement
s = sin(l);
the fact that the sin routine takes a
floating-point argument is not noticed
until the erroneous result is detected by
the programmer.
In the structure reference
p -> memb
p is simply assumed to point to a struc¬
ture of which memb is a member; p might
even be an integer and not a pointer at
all.
Much of the explanation, if not justifi¬
cation, for such laxity is the typeless
nature of C’s predecessor languages.
Fortunately, a justification need no
longer be attempted, since a program is
now available that detects all common
type mismatches. This utility, called lint
because it picks bits of fluff from
programs, examines a set of files and
complains about a great many dubious
constructions, ranging from unused or
uninitialized variables through the type
errors mentioned. Programs that pass
unscathed through lint enjoy about as
complete freedom from type errors as
do Algol 68 programs, with a few excep¬
tions: unions are not checked dynamical¬
ly, and explicit escapes are available that
in effect turn off checking.
Some languages, such as Pascal and
Euclid, allow the writer to specify that
the value of a given variable may assume
only a given subrange of the integers. This
facility is often connected with the usage
of arrays, in that any array index must be
a variable or expression whose type
specifies a subset of the set given by
the bounds of the array. This approach
is not without theoretical difficulties,
as suggested by Habermann. 4 In itself
it does not solve the problems of variables
assuming unexpected values or of ac¬
cessing outside array bounds; such things
must (in general) be detected dynam¬
ically. Still, the extra information pro¬
vided by specifying the permissible range
for each variable provides valuable
information for the compiler and any
verifier program. C has no corresponding
facility.
One of the characteristic features of
C is its rather complete integration of
the notion of pointer and of address
arithmetic. Some writers, notably
Hoare, 5 have argued against the very
notion of pointer. We feel, however, that
the facilities offered by pointers are too
valuable to give up lightly.
8.2.3 Syntax peculiarities
Some people are annoyed by the terse¬
ness of expression that is one of the
characteristics of the language. We view
C’s short operators and general lack of
noise as a benefit. For example, the
use of braces for grouping instead
of begin and end seems appropriate in
view of the frequency of the operation.
The use of braces even fits well into
ordinary mathematical notation.
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Terseness can lead to code that is hard
to read, however. For example,
* + + * argv
where argv has been declared char **argv
(pointer to an array of character pointers)
means: select the character pointer
pointed at by argv (*argv), increment it
by one (++*argv), then fetch the
character that that pointer points at
(* + + *argv). This is concise and efficient
but reminiscent of APL.
An example of a minor problem is the
comment convention, which is PL/l’s
I* ... */. Comments do not nest, so an
effort to “comment out” a section of
code will fail if that section contains a
comment. And a number of us can testify
that it is surprisingly hard to recognize
when an “end comment” delimiter has
been botched, so that the comment
silently continues until the next comment
is reached, deleting a line or two of code.
It would bemore convenient if a single
unique character were reserved to intro¬
duce a comment, and if comments always
terminated at an end of line.
8.2.4 Semantic peculiarities
There are some occasionally surprising
operator precedences. For example,
a » 4 + 5
shifts right by 9. Perhaps worse,
(x & MASK) == 0
must be parenthesized to associate the
proper way. Users learn quickly to
parenthesize such doubtful cases; and
when feasible lint warns of suspicious
expressions (including both of these).
We have already mentioned the fact
that the case actions in a switch flow
through unless explicitly broken. In
practice, users write so many switch
statements that they become familiar
with this behavior and some even prefer
it.
Some problems arise from machine
differences that are reflected, perhaps
unnecessarily, into the semantics of C.
For example, the PDP-11 does sign
extension on byte fetches, so that a
character (viewed arithmetically) can
have a value ranging from -128 to
+ 127, rather than 0 to +255. Although
the reference manual makes it quite
clear that the precise range of a char
variable is machine dependent, program¬
mers occasionally succumb to the tempta¬
tion of using the full range that their local
machine can represent, forgetting that
their programs may not work on another
machine. The fundamental problem, of
course, is that C permits small numbers,
as well as genuine characters, to be stored
in char variables. This might not be
necessary if, for example, the notion of
subranges (mentioned above) were intro¬
duced into the language.
8.2.5 Miscellaneous
C was developed and is generally used
in a highly responsive interactive environ¬
ment, and accordingly the compiler
provides few of the services usually
associated with batch compilers. For
example, it prepares no listing of the
source program, no cross reference table,
and no indication of the nature of the
generated code. Such facilities are avail¬
able, but they are separate programs, not
parts of the compiler. Programmers used
to batch environments may find it hard
to live without giant listings; we would
find it hard to use them.
IX. CONCLUSIONS AND
FUTURE DIRECTIONS
C has continued to develop in recent
years, mostly by upwardly compatible
extensions, occasionally by restrictions
against manifestly nonportable or illegal
programs that happened to be compiled
into something useful. The most recent
major changes were motivated by the
extension of C to other machines, and
the resulting emphasis on portability.
The advent of union and of casts reflects
a desire to be more precise about types
when moving to other machines is in
prospect. These changes have had relative¬
ly little effect on programmers who
remained entirely on the UNIX system.
Of more importance was a new library,
which changed the use of a “portable”
library from an option into an effective
standard, while simultaneously increasing
the efficiency of the library so that users
would not object.
It is more difficult, of course, to
speculate about the future. C is now
encountering more and more foreign
environments, and this is producting
many demands for C to adapt itself to
the hardware, and particularly to the
operating systems, of other machines.
Bit fields, for example, are a response to
a request to describe externally imposed
data layouts. Similarly, the procedures
for external storage allocation and
referencing have been made tighter to
conform to requirements on other
systems. Portability of the basic language
seems well handled, but interactions with
operating systems grow ever more com¬
plex. These lead to requests for more
sophisticated data descriptions and initial¬
izations, and even for assembler windows.
Further changes of this sort are likely.
What is not likely is a fundamental
change in the level of the language.
Realistically, the very acceptance of C has
compelled changes to be made only most
cautiously and compatibly. Should the
pressure for improvements become too
strong for the language to accommodate,
C would probably have to be left as is,
and a totally new language developed. We
leave it to the reader to speculate on
whether it should be called D or P.
REFERENCES
1. B. W. Kemighan and D. M. Ritchie, The C
Programming Language, Englewood Cliffs,
N.J.: Prentice-Hail, 1978.
2. M. Richards, “BCPL: A Tool for Compiler
Writing and Systems Programming,” Proc.
AFIPS SJCC, 34 (1969), pp. 557-566.
3. S. C. Johnson and B. W. Kernighan, “The
Programming Language B,” Comp. Sci.
Tech Rep. No. 8, Bell Laboratories (January
1973).
4. A. N. Habermann, “Critical Comments on
the Programming Language PASCAL,”
Acta Informatica, 3 (1973), pp. 47-58.
5. C. A. R. Hoare, “Data Reliability,” ACM
SIGPLAN Notices, 10 (June 1975),
pp. 528-533.
Number 45
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Page 29
Structured
programming,
Compound Statements
When you write a program, you write
a list of statements:
x = x - 1
a = b + c
b = b * 2 —c
x = b - a
The idea behind a compound state¬
ment is to make one statement—a mole¬
cule—out of a set of statements —some
atoms. This is done in tiny-c by
[ x= x-1
a = b + c
b = b * 2 — c
x = b - a ]
Anywhere you can write a simple
statement you can also write a compound
statement. This sounds simple, but the
effect is powerful. For example most
programming languages have an if state¬
ment similar to this:
BY T. A. GIBSON AND S. B. GUTHERY
tiny-c associates
P.0. Box 269
Holmdel, N.J. 07733
Perhaps you have heard structured
programming described as “go-to-less”
programming. Or programming with just
if-then-else and do-while control state¬
ments. Such remarks oversimplify what
structured programming is all about.
The essence of structured programming
is PROGRAM CLARITY. You can
write programs in small, modular parts
with easy-to-follow program flow. You
can use well-chosen, descriptive variable
names. This leads to clear, humanly
understandable programs. That is the real
objective of structured programming.
We discuss here three principle ideas
that make program clarity possible.
These are: modularity, predictable pro¬
gram flow, and local variables.
MODULARITY in software is just as
important as modularity in hardware.
It makes it humanly possible to deal
with complexity. A module is a brick
or atom used for building bigger modules.
Seen from within, a module may be
very complex but from the outside it is
an indivisible whole. Software modularity
is achieved through the use of FUNC¬
TIONS.
© 1980, tiny-c associates
PROGRAM FLOW is predictable if
you can point to any statement and easily
answer the question “under what condi¬
tions is this statement executed?” This is
particularly important if the program is
20 or 30 pages long and still has bugs.
Scanning the whole program and draw¬
ing arrows is no fair. That’s not consid¬
ered an easy way to answer the question.
Predictable program flow can be achieved
in many ways. In C, it is done with COM¬
POUND STATEMENTS.
Functions also make it possible to
hide variables used in a strictly local
context. The variable n is very popular;
it’s used frequently to count things.
Have you ever had a program blow up
because you were using n in two places
for two purposes? The fix was to change
one of them to nl. A better idea is in
the concept of LOCAL and GLOBAL
variables.
David Gries suggests structured pro¬
gramming be called “simplicity theory,”
and characterizes it as “an approach to
understanding the complete programming
process” [Gries 1974]. As a pleasant divi¬
dend, structured programming is more
enjoyable than monolithic programming.
It should certainly, therefore, be a part
of personal computing. To begin our look
at tiny-c as a structured programming
language, let’s look at the foundation of
functions and predictable program flow —
the compound statement.
if (logical expression) statement
So you can write
if(x>0) x = x — 1
But make the statement part compound,
and you have this capability:
if (x>0) [
b = b*2-c
a = b + c
x = x - 1
1
This multiline if is not some special
kind of if. It is still:
if (logical expression) statement
But the statement part is compound. The
compound statement is treated as an in¬
divisible unit. It is either all done or all
not done depending on the value of the
logical expression.
The compound statement also is a
natural for LOOPS. There is a big dif¬
ference among the various programming
languages in how you write loops, but
they all have one thing in common.
A loop has a beginning and an end.
A compound statement can be used to
express this. The looping statement is:
while (logical expression) statement
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Number 45
201
Notice the similarity with the if.
Only the keyword has changed. Here’s
how while works. The logical expression
is evaluated. If it is true, then the state¬
ment is executed, and then the while is
done again. The effect is a repeated if,
i.e., a loop. As long as the logical expres¬
sion remains true, the statement is done
again and again. Eventually something in
the statement causes the logical expres¬
sion to become false, and the loop
terminates. Of course, the statement can
be compound, as in:
while (x>0) [
a= b+c
b = b*2—c
x = x— 1
3
The compound statement is a natural
way to delimit the beginning and end of
loops.
With one simple idea, the compound
statement, two things are achieved. The
if statement is more powerful than is
common in non-structured programming
languages. The concept of a loop col¬
lapses to a simple repeated if or while
statement. In both situations you are
stating conditions under which the
statement — whether simple or com¬
pound—is to be executed.
Nesting Compound Statements
ANYWHERE YOU CAN WRITE
A SIMPLE STATEMENT, YOU
CAN WRITE A COMPOUND
STATEMENT
That is a fundamental rule. A compound
statement contains simple statements.
Therefore a compound statment can
contain compound statements. Figure 1
illustrates this.
FIGURE 1
[ x = x- 1
a = b+c
b = b* 2 — a
x = b—a
1
a= b+c is a simple statement. The rule says a
compound statement can be written here. For
example:
[ x — x 1
[ a=b+c
w=y+2*x+w
y -17
1
b = b*2—a
x = b-a
The substitution of a compound for a
simple shown in Figure 1 is certainly al¬
lowable, but is of no practical value.
The real utility in nested compounds is
in writing nested if and while state¬
ments. Figure 2 is therefore a more real¬
istic example of the use of compound
statements.
FIGURE 2
if(x>0) [
while (x <limit) [
if (case==l) [
y = 0; w = 99
I
if (case==2) [
y = 99; w = 0
]
nextaction
x = x+l
1
In Figure 2 if you remove everything
except the brackets, you have this:
[[[][]]]
This is what is meant by nested com¬
pound statements. Brackets are used to
form program units the same way paren¬
theses are used to create arithmetic state¬
ments. The main difference is that a
pair of brackets is preceded by a function
name, or a logical expression. In the first
case you’re naming the contents of the
brackets and in the second you’re stating
the conditions under which the contents
are to be executed.
Readable Program Flow
In Figure 2, look at the “y = 0” in
the fourth line. How can it be reached?
Only if case is 1, and x is less than limit.
No go-to can lead here, either accident¬
ally or on purpose.
How can “nextaction” be reached?
Only if x is less than limit, and then only
after possible changes to y and w. This
program has simple, predictable flow. The
only way a statement other than a
while can be reached is from directly
above. Whiles can also be reached from
their matching ] below.
Indenting and the Placement of Brackets
in Compound Statements
The brackets alone define the “struc¬
ture” of a program. Indenting means
nothing. But one of the purposes of
structured programming is to make pro¬
grams more readable and, hence, more
understandable. A good ghoice of in¬
denting style is very important to pro¬
gram readability. There are several styles
to choose from. The actual choice is not
too important. But once you choose a
style, stick to it. Consistency IS import¬
ant.
One easily explained style is to align
matching brackets vertically. This looks
like:
if (x>0)
[ statement
statement
»»
>>
A problem with this is that when editing
the first statement, care must be taken to
keep the [ intact. So some use this
style:
if (x>0)
1
statement
statement
This takes an extra line. Also there is
a visual break between the if and its
statements. So some take the left bracket
and move it to the end of the preceding
line:
if (x>0) [
statement
statement
The right bracket is now vertically
aligned with the if or while that pre¬
ceded the compound statement.
You may pick one of these, or invent
a style of your own. But, we repeat,
whatever you decide to do, do it con¬
sistently.
Functions
A large software project can usually
be broken into natural parts, and each
part programmed and debugged as a
separate unit. Each of these units then
becomes a reliable building block for the
construction of still larger parts of the
project. Sometimes units can be designed
to be useful in many projects.
In various programming languages
these building blocks are called subpro¬
grams, subroutines, or, as in C, FUNC-
Number 45
202
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 31
TilONS. Here is a tiny-c function for
any computer versus human game:
game [
getready
while (stillplaying ( ) ) [
humantum
if (stillplaying ()) computerturn
i
gameover
1
The name of the function is “game”.
The compound statement that follows
is called the body of the function. Each
[ can be read as “do all of this”, and its
matching ] read as “end of this”. Game
divides the design of a game program
into five parts:
getready (which initializes things, and
prints instructions if requested),
stillplaying (which determines if the game
is still going, and returns true if it is, other¬
wise false),
humainturn (which conducts the human’s
turn),
computerturn (which conducts the com¬
puter’s turn),
gameover (which computes and prints
scores, makes remarks about the human’s
skill, promotes the human, or whatever).
The game function is the first step in
divide-and-conquer or top-down pro¬
gram development. Let’s carry this
development one step further. The get¬
ready function can be expanded this way:
getready [
ps “Do you want instructions?”
if (gc () ==‘ y 0 instructions
]
Getready divides the initialization into
two parts: instructions, and setupboard.
(.Note : ps prints a character string, gc()
reads a character, and ==‘y’ tests if the
character is a y.)
Notice that both game and getready
are universal. They can be used in many
game programs. Programming in this
fashion eventually leads to a library of
useful, general purposes functions these
can be pulled off the shelf into a soft¬
ware project. You know they work be¬
cause they were used before. Your pro¬
gramming becomes more productive, and
more pleasant.
The next time you’re programming a
sizable project, i.e., anything more than
a page, try to identify subsets of the
logic usable in other projects. Capture
these as functions.
It is gratifying to discover a general
purpose function where none was
suspected.
Local and Global Variables
A LOCAL VARIABLE is one that is
known only inside a function. It can be
used and changed only within the body of
the function. Even its name is unknown
outside the function. In fact, its name
can be used in other functions without
conflict. This is what makes local vari¬
ables useful .
Take a look at Figure 3. There are
four local variables in these two func¬
tions. The variables n and maximum
are local to a function. The variables n
and total are local to anotherfunction.
If either of these functions calls the
other, the values of n will not be con¬
fused since they only have meaning in¬
side the body of their own functions.
It helps to think of local variable names
as being preceded by the possessive form
of the function to which they are local;
for example, afunction’s n and another-
function’s n.
FIGURE 3
afunction [
int n, maximum
n=0
while (n<maximum) [
n=n+l
1
1
anotherfunction [
int n, total
n = n + 2
total = total+n
1
The value of locals is obvious to any¬
one who has spent a nasty debugging
session trying to find out where, in a
huge program, some variable is getting
changed.
Of course not all variables can be
local. Some must be shared by many
functions. These are called GLOBALS.
They should be used infrequently, as
they do cause debugging headaches.
Choosing good, descriptive names for
globals alleviates the problem. A global
named “k”is inviting disaster. Call it
“klingonsleft” and you’re less likely to
accidentally use it for two purposes.
Also you’ve given a reader of your pro¬
gram a pretty good clue to the variable’s
use.
Summary of Structured Programming
These concepts: functions, locals and
globals, and compound statements are
probably the main tools of structured
programming. It’s really that simple.
Many variations and improvements are
possible. The most important improve¬
ment is to the concept of locals and
globals. This is a special case of the more
general notion of nested scope of vari¬
ables. But we will not go into that here.
Tiny-c and (BIG) C
The examples in this article all use
tiny-c. If you move to BIG C, there are
a few differences. Tiny-c is a training
language, just like BASIC. Technically,
it is a COGNATE of C, not a subset.
The syntax differences are:
In C, all statements must end with a semi
colon(;). In tiny-c they end with the end of
a line, or a ; or ].
or a ; or ].
In C, all functions must have parentheses
around the arguments. In tiny-c they can
frequently be omitted.
In C, compound statements use j } in¬
stead of [ ], array references use [ ]
instead of ( ).
So figure 2 in C looks like:
if (x>0){
while (x < limit){
if (case==l){
y = 0;w= 99;
I
if (case = = 2){
y = 99; w = 0;
I
nextaction ( );
x = x+1;
Notice that the function call nextaction
( ); must have the parenthesis, even with
no arguments. And the semicolons
shown must all be there.
The game function is written in C
like this:
game ( ) ; |
getready() ;
while (stillplaying ()) {
humantum () ;
if (stillplaying()) computerturn() ;
I
gameover() ;
I
There are also differences in the input/
output library functions. These differ¬
ences are less important than the syntax
differences, because in C input/output
is done with function calls, and not built
into the syntax of the language.
In C, to print an integer requires this:
printf ( “ %d”, x) ;
In tiny-c this suffices:
pn x
Page 32
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
203
Summary of tiny-c and C
In deriving a training cognate of C,
we moved to lower case characters ( [
instead of { ), removed punctuation
distracting to students, and introduced
much simpler input/output functions.
The resulting language, tiny-c, is as
easy to learn as BASIC, and serves as a
good stepping stone into structured
programming.
BIBLIOGRAPHY
Gibson, T. and Guthery, S., The tiny-c
Owner’s Manual , tiny c associates,
1978.
Gibson, Paul, “Stopwatch: A tiny-c
Program,” CREATIVE COMPUTING,
Vol. 5, No. 3 (March 1979).
Gibson, Tom, “Caution: Structured Pro¬
gramming Can Be Habit-Forming,”
CREATIVE COMPUTING, Vol. 5,
No. 1 (January 1979).
Gries, David, “On Structured Program¬
ming - A Reply to Smoliar,” CACM,
Vol. 17, No. 11 (November 1974).
Hancock, L., “Growing, Pruning & Climb¬
ing Binary Trees with tiny-c,” DR.
DOBB’S JOURNAL, Vol. 4, Issue 6
(June/July 1979).
Hancock, L., “Dear Doctors, ” letter
to DR. DOBB’S JOURNAL, Vol. 4,
Issue 3 (March 1979), on page 9.
Hancock, L., “Implementing a tiny inter¬
preter with a CP/M flavored C,”
DR. DOBB’S JOURNAL, Vol. 5,
Issue 1, (January 1980).
Kern, Christopher O., “A User’s Look at
tiny-c,” BYTE, Vol. 4, No. 12 (De¬
cember 1979).
Kernighan, Brian W. and Ritchie, Dennis
M„ THE C PROGRAMMING LAN¬
GUAGE, Prentice-Hall Software Series,
1978.
Madden, J. Gregory, “C: A Language for
Microprocessors?,” BYTE, Vol. 2,
No. 10 (October 1977).
Newberry, Steve, “A Great Way to
Learn Structured Programming, tiny—
c,” part of the article “An Overview
of CP/M Compatible Software,” DR.
DOBB’S JOURNAL, Vol. 5, Issue 1
(January 1980).
Nussbaum, Frank, “Reader Cs Pascal
Alternative,” letter to BYTE, page
142, Vol. 3, No. 11 (November
1978).
Shapin, Ted, “Review of tiny-c Owner’s
Manual,” DR. DOBB’S JOURNAL,
Vol. 4, Issue 2 (February 1979).
Zahn, C. T., C NOTES: A Guide to the
C Programming Language , Yourdon
Press, 1979.
Number 45
204
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 33
HELP
'WITH
BY LEE BARKER
Chicago, II.
OSil’s Fortran, Basic, and Cobol CP/M package was
purchased a year ago and a number of problems encountered.
The most serious of these being that Cobol wouldn’t work.
Last month the updated version was obtained with some of
the old problems fixed, and a few new ones added. Enclosed is
a modified hsting of the OSI’s 10 routines that corrects a few
of the se problems.
Not covered here is the most serious problem with the new
operating system. There is a routine in 6502 code, 81 bytes
into track 0 to initialize the 16 ports starting at 0CF00H.
CP/M in loading overwrites these ports. If these ports are used
before being re-initialized the system will lock.
Other problems include—control S works perhaps 20% of
the time, but not at all in basic. Microsoft’s Basic was designed
for the 8080 using the IN, OUT instructions. Since the OSI
uses ACIAs Basic’s IN, OUT, WAIT do not work. Also if the
control character 9 is needed for cursor addressing or the
printer, a string of CHR$(32)s will be obtained instead.
(TAB) As an alternative, the CURSOR.ASM listing is a
method of associating a string directly with an address on the
screen. This simplifies building screens in that only one
variable is needed to describe a string and its location rather
than the usual four.
I hope these listings will provide some help to others who
may have had similar problems.
P.S. To Re-init ports
Fix:
LXI
H,0CF2O
DCR
L
DCR
L
MVJ
M,3
MVJ
M,17
JNZ
Fix + 3
99
^ *100
m
title 0S1B10S.ASM
Rewritten 1-0 routines for the 0S1 witn CP/M
Set up for CRT at 0FC00H
LPT at 0CF00H
MODEM at 0CF02H
Problems with system as delivered:
1. "S usually didn't worn witn CP/M
2. “S didn't wor* at all in basic
3. ChR»(y) prints as a string o t spaces
4. OSl uses ACiA's so iN OUT A WAiT oon't work
5. Program's must be rewritten to redirect output
b. Track 0 initialized the lb ports at UCFQ0H
which CP/M in loading would clobber.
if any of tnem were used, tne system wou-Ld lock.
Corrections:
; are for #1 to
5. #0 is handled seperateiy.
BE00
ORG 0BE00H
; jump table
FC00
=
CRT EQU
OFCOOH ; Main terminal port
CF00
s
LPT EQU
0CF00H ; Line printer
; CP/M jump table
BE00
CD2DBE
START: CALL
CONT ; Cold
BE03
CD2DBE
CALL
CONT ; Warm
BE06
C300BF
JMP
READY
BE09
C309BF
JMP
TTY IN
BE0C
C316BF
JMP
TTYOUT
BE0F
C328BF
JMP
PRINT ; Line printer
BE 12
C345BF
JMP
POUT ; Peripnerai
BE 15
C336BF
JMP
PIN
BE 18
CD2DBE
CALL
CONT
BE IB
CD2DBE
CALL
CONT
BE IE
CD2DBE
CALL
CONI
BE21
CD2DBE
CALL
CONI
BE24
CD2DBE
CALL
CONT
BE27
CD2DBE
CALL
CONT
BE2A
CD2DBE
CALL
CONI
C0NT:
BF00
ORG 0BF0OH
; CP/M OSl 1-0
; Was a key pressed on the CRT/
BF00
3A00FC
READY: LDA
CRT
BF03
IF
RAR
BF04
3EO0
MV1
A.O
BF06
DO
RNC
BF07
3D
DCR
A
BF08
C9
RET
; Input a character from the CRT.
BF09
3A00FC
TTYIN: LDA
CRT
BF0C
IF
RAR
BF0D
D209BF
JNC
TTY IN
BF10
3A01FC
LDA
CRT*1
BF13
E67F
AN1
127
BF15
C9
RET
; Output a character to the CRT.
BF16
F5
TTY0UT: PUSH
PSW
BF17
3A00FC
LDA
CRT
BF1A
IF
RAR
BF1B
DA57BF
JC
TEST
BF1E
IF
RAR
BF1F
D217BF
JNC
TTYOUT*1
BF22
79
MOV
A, C
BF23
3201FC
STA
CRT*1
BF26
FI
POP
PSW
BF 27
C9
RET
; Output a character to tne line printer.
BF28
E5
PRINT: PUSH
H
BF29
F5
PUSH
PSW
BF2A
2A53BF
LHLD
ADDR
BF2D
7E
PL00P: MOV
A.M
BF2E
IF
RAR
BF2F
IF
RAR
BF30
D22DBF
JNC
PLOOP
BF
23
1NX
H
BF34
71
MOV
M, C
BF35
FI
POP
PSW
BF36
El
POP
H
BF37
C9
RET
; Input a chr.
from tne modem (ADDH+2)
6F30
2A55bF
PIN: LHLD
AODR+2
BF3B
7E
MOV
A.M
bFjC
IF
RAR
BF3D
D2JBBF
JNC
PIN*.}
BF40
23
1NX
H
BF41
7E
MOV
A ,M
BF42
E67F
AN1
127
BF44
C9
REI
; Output a chr.
to the modem.
BF45
2A55BF
POUT: LHLD
ADDR*2
£
Page 36
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
205
101
BF48
F5
PUSH
PSW
102
BF49
7E
MOV
A,M
103
BF4A
IF
RAR
104
BF4B
IF
RAR
105
BF4C
D249BF
JNC
POUT-*.4
106
BF4F
23
INX
H
107
BF50
71
MOV
M,C
108
BF51
FI
POP
PSW
109
BF52
C9
RET
110
;
111
BF53
00CF00CF
ADDR: DB
00,207,00,20/
112
;
113
; Test for what
key was entered.
114
BF57
3A01FC
TEST: LDA
CRT+1
115
BF5A
Eb/F
AN1
127
116
BF5C
FE13
CPI
19 ; “S
117
BF5E
C217BF
JNZ
moui +1
110
BF61
C357BF
JMP
TEST
119
;
120
; Single entry
point for the following routines.
121
BF64
3D
USR: DCR
A
122
BF65
3D
DCR
A ; If passed integer
123
BF66
CA79BF
JZ
1NTEG ; Print CHR$(integer mod 25b)
124
BF69
3D
DCR
A
125
BF6A
CA7DBF
JZ
STRING ; Print exact string to LPT
126
;
127
; Input a single character.
128
BF6D
CD09BF
CHAR: CALL
TTY IN
129
BF70
6F
MOV
L, A
130
BF71
2600
MV I
H,0
131
BF73
E5
PUSH
H
132
BF74
2A0501
LHLD
0105H
133
BF77
E3
XTHL
134
BF/8
C9
RET
135
;
136
; Print the CHR
passed as an integer 0-255.
137
BF79
4E
1NTEG: MOV
C,M
138
BF7A
C316BF
JMP
TTYOUT
139
;
140
; Print a string to tne line printer (inc Chn*(y)).
141
BF 70
EB
STRING: XCHG
142
BF7E
46
MOV
B,M
143
BF/F
23
1NX
H
144
BF80
5E
MOV
E,M
145
BF81
23
1NX
H
146
BF82
56
MOV
D,M
147
BF83
EB
XCHG
148
BF84
04
1NR
B
149
BF85
05
SLOOP: DCR
B
150
BF86
C8
RZ
151
BF87
4E
MOV
C,M
152
BF88
23
1NX
H
153
BF89
CD00CF
CALL
LPT
154
BF8C
C385BF
JMP
SLOOP
155
;
156
BF8F
END
2
3
; title
CURSOR.ASM
4
; USR call to
print string with direct cursor addressing.
5
; String is in
the form "#yyxx."
7
BFlO
=
CRT EQU
OBFIbH ; prints to CRT reg. C
8
BF09
=
CRT1N EQU
0BF09H ; Returns entered key in reg a
10
BFb4
ORG 0BF64H
12
BFb4
3D
START: DCR
A
13
BF65
3D
DCR
A ; integer passed'.'
14
BFbo
CA/9BF
JZ
1NTEG ; Yup
15
BFo9
3D
DCR
A
16
BF6A
CA/DBF
JZ
STRING
17
BF6D
CD09BF
CALL
CRTiN
18
BF70
6F
MOV
L, A
19
BF71
2600
MVi
H, 0
20
BF73
E5
PUSH
H
21
BF74
2A0501
LHLD
0105H ; MAKiNT
22
BF77
E3
XTHL
23
BF 78
C9
RET
24
;
25
BF79
4E
1NTEG: MOV
C,M
26
BF7A
C316BF
JMP
CRT
27
;
28
BF7D
EB
STRING: XChG
29
BF7E
7E
MOV
A, M
30
BF7F
40
MOV
B,M
31
BFoO
04
1NR
B
32
BF81
23
1NX
H
33
BF02
5E
MOV
E,M
34
BF83
23
1NX
H
35
BF84
5o
MOV
D,M ; DE points to string
36
bF85
EB
XCHG
37
BF86
FE05
CPI
5 ; A = ien.
BF88
DABEBF
JC
SKIP
39
BF8B
7E
MOV
A, M
40
BF8C
FE23
CPI
35 ;
41
BF8E
C2BEBF
JNZ
SKIP
» =-= 7
4
42:
BF91 E5
PUSH
H
; save in case plain string
43:
BF92 CDC8BF
CALL
TEN
44:
BF95 D2D9BF
JNC
FAIL1
; Y wasn't numeric
45:
BF98 83
ADD
E
46:
BF99 FE18
CPI
24
; Y
47:
BF9B D2D9BF
JNC
FA1L1
; Y > 0 to 23
48:
BF9E 57
MOV
D, A
49:
BF9F CDC8BF
CALL
TEN
50:
BFA2 D2D9BF
JNC
FA1L1
; X wasn't numeric
51:
BFA5 83
ADD
E
52:
BFA6 FE50
CPi
80
53:
BFA8 D2D9BF
JNC
FA1L1
; X > 0 to 79
54:
BFAB 0E14
MVI
C,20
; Cursor address code
55:
BFAD CDIbbF
CALL
CRT
56:
BFBO 4A
MOV
C,D
57:
BFB1 CD16BF
CALL
CRT
58:
BFB4 4F
MOV
C, A
59:
BFB5 CDIbbF
CALL
CRT
oO:
BFB8 23
1NX
H
; first byte of string
61 :
BFB9 D1
POP
D
; didn't need it
62:
BFBA 78
MOV
A ,B
63:
BFBB D605
SU1
5
64:
BFBD 47
MOV
B, A
65:
BFBE 05
SKIP:
DCR
B
66:
BFBF C8
RZ
; done
67:
BFCO 4E
MOV
C,M
68:
BFC1 23
INX
H
69:
BFC2 CD16BF
CALL
CRT
70:
BFC5 C3BEBF
JMP
SKIP
71:
BFC8 CDD2BF
TEN:
CALL
TEST
72:
BFCB DO
RNC
73:
BFCC 07
RLC
74:
BFCD 5F
MOV
E,A
75:
BFCE 07
RLC
76:
BFCF 07
RLC
77:
BFDO 83
ADD
E
; times 10
78:
BFD1 5F
MOV
E, A
79:
BFD2 23
TEST:
INX
H
80:
BFD3 7£
MOV
A ,M
81:
BFD4 D630
SU1
40
82:
BFD6 FEOA
CPi
10
83:
BFDO C9
RET
84:
85:
BFD9 El
FA1L1:
POP
H
86:
BFDA C3BEBF
JMP
SKIP
; print string
87:
88:
BFDD
END
Number 45
206
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 37
BY DENNIS ALLISON Associativity: ao(boc) = (aob)oc for
all a, b, c in the group.
ALGORITHMS Identity Element: there is an element
i in the group such that aoi=ioa = a
Algorithms are published in many for any a in the group,
places. For many years there was an Inverse Element : for any a in the
algorithms column in the Communica- group there exists an element a' in the
tions of the ACM (it’s now published as group (the inverse of a) such that
pari: of ACM’s Transactions on Mathema- a° a’ = i
tical Software). I learned a lot reading
those algorithms and trying to understand jf one a i so has the ax i om
how they work); they are still worth
reading and understanding. Commutativity: aob = boa for all a
and b in the group.
BLOCK INTERCHANGE
then the group is an Abelian group and
Suppose we have an array of N objects a number of useful and interesting pro-
which we partition into two parts, one perties follow immediately,
with m objects in it and the other with Consider the additive group of integers
n - N - m. The problem is to interchange modulo N. The elements of the group are
the two parts with a minimum of data the integers 0, 1, . . . , N—1. The opera-
moves and no significant temporary tion is ordinary addition except that
storage. Symbolically we can represent results greater than or equal to N are
the task as reduced by N.
If we partition N into two elements so
that N = m + n, then the elements 0, n,
2n, 3n, . . . form a cyclic subgroup. A
subgroup is simply a subset of the ele¬
ments of a group which themselves form a
group. A cyclic group is one which for all
elements in the group
aoaoao ...o a = a
for some number of repeated operations.
The number of operations required is
called the order of the group. For our
group this is given by N/gcd(m,n) where
1 N gcd(m,n) is the greatest-common-divisor.
Each of the elements 1, 2, 3,. . . belongs
1 he program below is a modification to a distinct coset of the group and form
of an algorithm published by Walter a disjoint covering. There are, of course,
Fletcher [ACM Algorithm 284, CACM gcd(m.n) cosets.
9:5, May 1966] based upon some results Fletcher’s published algorithm com-
of group theory. puted the gcd(m,n) and then ran two
A group is a mathematical system loops: an outer loop which selected one
consisting of a non-empty set of elements of the cosets and an inner loop which
and a single binary operation, o, which selected an element, interchanged it with
obeys the axioms: the next generated element of the sub¬
group n locations forward (modulo
N) and continued until the entire coset
was moved.
My version of the algorithm, pro¬
grammed below in C, does not compute
the gcd. Again, there are two loops: an
outer loop which simply counts the total
number of interchanges which must,
eventually, equal N. The inner loop
simply looks for the periodic return to
the initial value and then selects the next
coset. All in all, an elegant solution with
only N interchanges.
SAVING THE POINTER IN DOUBLY
LINKED LISTS
A doubly linked list consists of nodes
which contain two pointers and the
associated data. One pointer points
forward to the next list node; the other
points backward to the previous node:
The flexibility of a doubly linked list is
often offset by the additional storage
required for the second pointer. For
many algorithms which traverse doubly
linked lists one can use a trick and save
the storage space required for one of
the pointers.
Page 38
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
207
The trick relies upon a property of the
exclusive-or operation which is available
on most computers. For any numbers a
and b one has
a = (a A b) A b ,
where A is the exclusive- or operator.
The trick is to store the exclusive-or of
the FWD and BKWD pointers at each
node. Traversal of the list then requires
three pieces of information: the old
direction, the address of the current node
(to decode the next node), and the
address of the last node visited.
To see how this works, suppose we
are at node N 5 and we’ve just come from
node N 4 so both addresses are available.
Using Nj to indicate the address of the
node, the contents of the link fields
would be
N 3 A n 5
N s :
n 4 a n*
N 6 :
n s a n 7
Data
Data
Data
and we could get a forward move by
n 6 = n 4 a (N 4 a n 6 )
and a backwards move directly from the
stored address. Of course one would have
/
to update the window information to
allow successive moves in any direction.
Notice that the program must know
something of the list structure in order
to interpret the pointer field. Considered
just as values they are inscrutable!
I don’t know much about the history
of this trick. Charles Wetherell (author
of “Programming Pastimes and Pleasures”
in this journal) showed it to me with
considerable glee some years ago; he’d
found it, if memory serves, in block
memory allocation and recovery support
system in an operating system.
Number 45
208
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 39
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MITS DOS
Disk to Disk
Copy Routine
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BY ANDREW L. BENDER, M. D.
Neurological Services Inc.
Westwood, NJ 07675
Often there is a need to prepare floppy disks, or removable
packs, with sets of “standard” predetermined files. One
example is the construction of “library disks;” another is the
preparation of distribution copies of programs. Being in the
position of needing both library disks and distribution disks I
had used the “COP” routine supplied with MITS DOS. This
routine is: quite fast and very flexible; however, it is difficult
to use. It must be invoked each time you want to copy a
single file:; six parameters must be given for each file copied.
If anything goes wrong during the copy or assignment of
files, the routine unforgivingly aborts with little or no informa¬
tion as to why it failed.
In order to remedy the above faults and ease the burden of
preparing libraries, I wrote a disk to disk copy program which
I call “CPY.” CPY will accept a list of files to be copied in a
text file which you, the user, prepare with the text editor
“EDIT” system program. The list of files gives the name
and disk number of each file to be copied. The CPY program
is given the number of an output disk and the files in the list
are copied one by one to that disk. Once the copy has started
there is no need for the user to intervene. The files must
retain the same name on the output disk as on the input disk.
During the copy several things are checked and certain
actions are taken. If a file is specified as being on the output
disk in the list, no copy will occur. In the case of a file being
specified to be copied onto the output disk when it already
resides on the output disk, no copy will occur. If a file cannot
be found to be copied, the directive is just ignored as if it were
not present. An I/O error will abort the copy.
The philosophy in structuring the error checking and
handling was that the routine was going to be used only by
people familiar with files, file structures and data processing.
It was not written to be used as an application program by a
general user. Whenever an error occurs during processing
the error code number is printed along with the file number
on which the error occurred.
Use of CPY
To call the program:
^ CPY textfilename, textfile disk, outputdisk
( ^ supplied by DOS)
Where textfilename is the name of the list of files prepared
with the text editor program. Note that the leading ampersand
(&) in the file name should not be included as CPY will supply
this internally. Textfile disk is the disk unit on which the file
list can be found. Outputdisk is the number of the disk onto
which the files will be copied. For example if you wish to
copy the files specified in RLIBS on disk zero to disk one the
caU would be: ^CPY RLIBS,0,1
Let’s carry the example along: Suppose the file directory of
disk zero looked like this: *HEXOUT *OCTOCT *OPEN$
*HAZ2000 #LINK #ASM #EDIT #CPY #FDMP
#ABSDMP #LDR #MAP &RLIBS &MAPSYM &BLANG
&CP Let’s further assume the directory of disk one looked
like: #INIT #LINK #DEBUG #EDIT #CNS #COP
#ASM Let’s further assume that RLIBS on disk zero looked
like:
00100 *HEXOUT, 0
00110 *DECOUT, 0
00120 *OCTOCT, 0
00130 #CPY, 0
00140 #ASM, 0
Now let’s trace the operation of the routine: Processing the
first file in the list (*HEXOUT, 0) the CPY program will
copy its text from disk zero to disk one. The next file
*DECOUT will not be found on disk zero, so a message that
the requested file wasn’t found on the input disk will be
printed. The program will then examine the requests on lines
120 and 130 copying the text of both files from disk zero to
disk one. At line 140 the file # ASM is already on disk one so
it will not do any copy. The CPY program will then exit to
DOS since line 140 was the last line in the file.
Page 40
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
209
DISK CONTROL
Just prior to initiation of copy, the program will ask if the
output disk is to be unloaded. At this time, if you want to put
a disk on the output drive you should change the disk before
typing in the response which can be Y or N. If you state Y, the
disk will be dismounted, then an immediate mount will be
issued. It is this action that makes it necessary to physically
change disks before answering the message. You can, of
course, rewrite that portion of the program if that annoys you,
but it seems to be the fastest way to handle it. Keying in “N”
assumes that you want to copy onto the current output disk.
PROGRAM DOCUMENTATION
The program listing documents what is happening here. I
used several undocumented MITS DOS entry points. They are
documented in the appendix. Two text messages in DOS were
also used: 010A6H is the start of “ENTER FILE NAME”
and 0101DH is the start of “ENTER DRIVE”. Two param¬
eters used in DOS were also used: 01321H which is a byte
containing the highest disk number and 01322H is a byte
which says how many sequential files are permitted. I would
recommend putting all of these entries into your SYSENT
element. I called the number of disks ND$$$ and the number
of files NF$$$.
PROGRAM TESTING
I tested this program for about a month on a two drive
system. I never tested it on drive numbers higher than 1. I
think it will work without problems because I used the conver¬
sion subroutines for larger numbers. It is a real pain getting a
routine up and running only to find that you have become
part of the debugging. I tried to avoid putting the user in this
position. There doesn’t seem to be any problem, but if you
find one please let me know. One note of caution concerns
attempts to copy the list of files with this program. Remember
that during program operation the list of files (FILE #3) is
open for input. This condition will not allow you to open this
file as an input file (FILE #1) for copying. You can handle
this situation in two ways: Use COP to copy the file or prepare
a second identical file on the input disk. I don’t feel this is a
bug, just a limitation imposed by DOS.
AVAILABILITY
I can supply a copy of the program and its accompanying
routine on your clean, error-free, HARD SECTORED MITS
FORMAT 8” disk. You must send the disk in a reusable
mailing container. A chipboard box will be fine. Please enclose
$8.00 to cover postage and handling in money order or cash.
We cannot accept stamps, checks or any requests from any
foreign countries with “black lists.” You are free to distribute
this program for any NON-COMMERCIAL use, but you may
not modify it or use it for commercial use without expressed
permission in writing from Neurological Services Inc. This
distribution notice must accompany ALL copies made for
distribution.
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APPENDIX
This is a narrative description of some non-published
entry points in MITS DOS. Not all of these entry points
are described.
Address Description and SYSENT label name
[Neurological Services System]
X’005 D’ LDEM - Loads the DE register pair from the
memory locations pointed to by the HI,
register pair. HL is incremented by two on
exit. (m,m+l) are loaded into DE.
X’006E’ MOVE8—Moves eight bytes from DE to HL.
BC = 0 on exit. DE and HL are updated.
X’0071’ MOVE—Moves the number of bytes con¬
tained in BC from DE to HL on exit DE and
HL are updated and BC = 0.
X’10A6’ [NOT IN OUR SYSENT] -An ASCII String
“ENTER FILE NAME” used by MSG,
ASKSS and other routines. CR/LF precede:
the message and it ends with the high order
bit set.
X’lOlD’ [NOT IN OUR SYSENT] - An ASCII String
“ENTER DRIVE” similar to the above
string in construction.
X’02EE’ CCEL1 —Conversion cell for binary to ASCII
conversion. Used to set base of conversion to
either 8 or 10 depending on how you want
the output (octal or decimal).
X’02EC’ CCELL—See above. You set both of them
before use.
X’02B7’ BINCVS —Converts the contents of HL to an
ASCII digit string in memory. If CCELL and
CCEL1 are set to 10, conversion is decimal
and if they are set to 8, conversion is octal.
The call to this subroutine should be fol¬
lowed by a DW containing the address of
where the first of the six digits of ASCII is
to be stored. An example:
CALL BINCVS ; DO CONVERSION
DW ASCOUT ; WHERE THE ASCII
GOES
X’OF75’ ASKSS—This subroutine is used to get the
first or next parameter from a processor call.
It must be followed by a DW which de¬
scribes a string to be output in the event that
the parameter is missing. On return, DE is
pointing to the first byte of the parameter.
If ASKSS finds a C/R code (x’OD’) it will
output the message described at the DW and
wait for a response to be typed in.
X’OFBE’ AANSS-Converts ASCII characters to DE
to binary. Result in A register on exit. This
must be followed by an error retijrn address
in case an error in conversion occurs, the
program will jump to the error return
address. Conversion stops on a comma,
blank or C/R.
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Number 45
210
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 41
X
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Number 45
214
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 45
ADDENDUM
De ar DDJ:
I was reveiwing the CPM printer driver which I sent you
and which you have indicated might be used in your August
issue, and have found one potential problem for some users.
I would advise that the following be used as an addendum to
the program DIABLO . PRN.
The program DIABLO contains one potential problem
which is evidenced when the DIABLO keyboard is used as the
console input device. If the console device is switched back
to the primary device while a CONIN input is being made,
a garbage character is read, since the status port is changed
but the data port does not change until the routine is re-en¬
tered. To correct this problem, the assembly listing should be
changed to show a jump to CONIN when the status shows
not ready instead of looping to CON3. The correct listing
should be:
020C CA9BD4 JZ CONIN + BASE L Loop till ready
In the article, I mentioned using Control P to turn a printer
on and off as CDOS does. I have just finished a modification
to my CPM CBIOS which adds this and several other features.
I will pass this along at my next opportunity.
Yours truly,
Steve
Pa<|e 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
215
an 0000 to Z0O translator system
BY ROBERT W. DEA
198 Lloyd Ave.
Fremont, Ca 94536
This program will accept 8080 mnemonics as input and
translate them to the corresponding Z80 mnemonics; it was
written in Digital Group Business Basic. I currently own a
Digital Group Z80 computer system with the 50K bytes of
memory, 4 digital PHI decks, and a 30 cps printer.
The 8080 to Z80 translator consists of a language skeleton
and a grammar analyzer. The language skeleton in this case
defines the structure of Intel 8080 mnemonics and the modi¬
fied Digital Group Z80 mnemonics. The grammar analyzer
parses the language skeleton in a top down left right process
and verifies the correctness of the input mnemonic and
generates the corresponding Z80 output. The translator is
totally driven by the language skeleton and can be easily
changed to translate a subset of the Z80 mnemonics to 8080
mnemonics. In fact it can be modified to perform any transla¬
tion which consists of a one-to-one transformation.
This version Can edit 8080 mnemonics and store them into
a tape file on my Digital Group system. It will read the edited
8080 file generated and translate the mnemonics to the modi¬
fied Digital Group Z80 mnemonics and store them into
another tape file for later input to my Z80 assembler. The
difference between the Digital Group Z80 mnemonics and the
Zilog mnemonics are those instructions that deal with the
accumulator. A few simple changes to the skeleton will allow
the generation of Zilog Z80 mnemonics.
The skeleton definition has the following format.
n,8080mn,Z80mn,sub1,sub2, . . .
n
8080m n
Z80mn
subn
The number of subfields following
The 8080 instruction
The Z80 equivalent instruction
Subfield definitions
<A> — regular one to one register translation
<33> — RST number translation
<CB> — register pair translation
<C> — register pair to accumulator
<K> — accumulator to register pair
<CE> — edit a comma
<F> — edit following character string to output
<3»> — one to one character string translation
The data scanner ends its scan upon detecting a 999 in the
(n) field. By removing these DATA statements and deleting
the speed enhancement section along with the comments
should reduce storage requirements by 30-40 % but increases
translation time by 100-150%.
TYPE (E) TO EDIT A 8080 SOURCE FILE
TYPE <T) TO TANSLATE 8080 TO Z80
>E
8080 EDIT PROGRAM
OUTPUT FILE ALWAYS ON DRIVE B1
TYPE 8080 SOURCE IN FOLLOWING FORMAT
LABEL OPERATION OPERAND COMMENT
TYPE '*EXIT' TO EXIT TO MENU
INPUT 8080 OUTPUT FILE NAME? TEST
OUTPUT FILE TEST WILL BE ON DRIVE B1
? MOV B»B
? MOV BfM
? MOV Mr C
? NLT
? MVI Br1
? MVI Mr 1
? LXI Bf377
t LXI SP077
? STAX B
? LDAX B
? SHLD 277
? LHLU 277
? STA 277
? LDA 377
? XCHG
? SPHL
? ANA B
? ANA M
? XRA B
? XRA M
? ORA B
? ORA M
? CMP B
? RLC
y RRC
? RAL
? RAR
? CMA
? STC
? CMC
y ani i
? XRI 2b
y 0RI 17
? CPI 7
y jnz label
y JZ LABEL
? JNC LABEL
? UC LABEL
? JP0 LABEL
? JP LABEL
? JM LABEL
? CNZ LABEL
? CZ LABEL
Number 45
216
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 47
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
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Number 45
218
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 49
1
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
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Page 5S2
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
etters
• L
EASING MICROSOFT GLITCHES
Dear DDJ:
This letter is about a number of problems in interfacing the
routine to basic as an example for your magazine.
Microsoft basic with CP/M was ordered from Lifeboat thru
a local dealer and was finally delivered this month. There were
a few problems, however. The most bothersome:
1. The printer was set up for a port that didn’t exist on my
system.
2. The ports starting at CFOO were initialized by track 0
correctly but then clobbered by CP/M in loading, so that
when any of those ports were used the system would lock
up.
3. The OSI machine uses ACIA’s not the Z-80 ports for 10.
This means that the Altair basic’s IN OUT WAIT will not
work.
4. If a CHR$(9) is printed (or LPRINTED) what is actually
printed is a string of CHR$(32)s.
Problems one and two were corrected by rewriting the
system’s I/O routines. (BEOO & BFOO). Since these routines
were being replaced, another routine was added to solve
; If A=2 then
position cursor (CRTOUT prints reg
BF75
0E14
INTEG: MVI
C,CURSE
BF7 7
CD0000
CALL
CRTOUT
BF7A
4E
MOV
C t M
value of Y
BF7B
CD0000
CALL
CRTOUT
BF7E
23
1NX
H
BF7F
4E
MOV
C r M ;
value of X
BF80
C30080
JMP
CRTOUT
; If A=3 then
print string
l to LPT (even CHR$(9))
BF83
EB
STRING: XCHG
pointer now in HL
BF84
46
MOV
B , M
B*len of string
BF85
04
INR
B
If B=0
BF86
23
1NX
H
BF87
5E
MOV
E,M
BF88
23
I NX
H
BF89
56
MOV
D, M }
got string address
BF8A
EB
XCHG
in regs HL
BF6B
05
SLOOP: DCR
B
end yet?
BF8C
C6
RZ
BF8D
4E
MOV
C i M
BF8E
23
1NX
H
BF8F
CD95BF
CALL
LPT ;
print a byte
BFy2
C38BBF
JMP
SLOOP
; Routine of
how LPT could look
BF95
E5
LPT: PUSH
H
BF96
F5
PUSH
PSW
BF97
2AA5BF
LHLD
ADDR ;
since all the ports are
BF9A
7E
MOV
A, M
handled the same
BF9B
E602
AN I
MASK I ;
this output is easily
BF9D
CA9ABF
JZ
LPT+5 ;
red i rected
BFA0
23
INX
H
BFAl
71
MOV
M,C
BFA2
FI
POP
PSW
BFA3
El
POP
H
BFA4
C9
RET
BFA5
00CF
ADDR: DB
00,0CFH
BFA7
END
problems three and four. In Basic ten USR calls are allowed. ‘ c
When the call is executed, register A contains the type of 2 a defin? £ togam tor USR calls
parameter passed (2=integer, 3=string, etc.). If A=2 then £ ehbfe*
HL will point to the number. If A=3 then DE will point
to the length of the string (same as VARPTR). By passing
different parameters one USR call can be made to handle
several routines. The following program will print a string
to the printer if passed a string. It will input one ASC
(character) entered on the keyboard if passed a single or
double precision number, or will position the cursor if passed
an integer (Y+X*256). I hope these routines may be of
some use to someone.
Yours truly, 2305 W. Winona
SB I
6k) INPUT"Position cursor
7u 1NPU1"Posit ion cursor
80 C-CY + CX*256
*0 OUSRU(C)
100 PRINT "Done";
110 :
120 PRINT CHR$(5);
130 CY « USR0(Z)
140 CX * USR0(Z)
150 PRINT "X*"; C\25b
160 PRINT"Y*"; C MOD 256
170 :
180 PRINT "A key? ";
190 C « USR0(Z)
200 PRINT "Thank you."
210 :
220 LINE INPUT"A string?
230 S - USR0(S)
240 END
L. Barker
Chicago, Ill. 60625
; OSI correction available as a USR call in BASIC CP/M
BF60
ORG
0BF60H
0000
=
CRT IN
EQU
0000H
; fill in value
0000
*
CRTOUT
EQU
0000H
; fill in value
0014
*
CURSE
EQU
14H
; position cursor control
0002
*
MASKI
EQU
2
; input port ready status
BF60
3D
START:
DCR
A
BF61
3D
DCR
A
BF62
CA75BF
JZ
INTEG
; A=2
BF65
3D
DCR
A
BF66
CA83BF
JZ
STRING
; A-3
BF69
CD0000
CALL
CRT IN
; get one character
BF6C
6F
MOV
L, A
; and pass it back
BF6D
2600
MV I
H, 0
; to basic
BF6F
E5
PUSH
H
BF70
2A0501
LHLD
0105H
; OSI's return integer
BF7 3
E3
XTHL
; address
BF74
C9
RET
MAKING A GOOD THING WORK
Dear DDJ,
Mark Zeiger’s program in DDJ #41 for changing XEK files
to CP/M files was very good. Except for the fact that it would
not work on my XEK files, it really was well written and
extremely valuable. This was my first exposure to CP/M and
Mark’s piece cleared up a lot of confusion on my part. My
Northstar system was bought secondhand with no guarantees
to the usefulness of the software. Without Mark’s fine article,
CP/M would still be an unknown quantity to me. Now at least
I have my feet wet.
Number 45
222
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 57
I think the problem is within my XEK files. It looks like
XEK treats the first three spaces encountered after the (1)
length byte; (2) fine number; and (3) dummy character
(space), as field delimiters. Mark’s program only expanded the
first space to a tab and all others were left as spaces. The
enclosed listing of the critical program area shows how I
adjusted the original program to fix my XEK files. I also
put in a (;) comment delimiter after the third tab for con¬
tinuity. (My XEK treats all data after the third tab as
comments with or without a field delimiter character).
Finally, there are at least two other areas of incompatabifi-
ty. First, in XEK all label references are truncated to five
characters for comparisons but are left full length in the source
files. Therefore ‘MACHINE’ in the label field would be evalu¬
ated as ‘MACHI’ and ‘MACHINE’ in the operand field will
reference ‘MACHI’ in the label field. In the CP/M assembler
more characters are compared and this causes ‘U’nidentified
errors.
The second problem has to do with negative referencing.
Since I use a Z-80 CPU but no Z-80 software, I simulate
relative jumps with the Z-80 code for the particular relative
jump followed by a computed offset.
JRZ
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STAT
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03H
MASK
*
EQU
02H
*
TTYOT
IN
STAT
ANI
MASK
DB
JRZ
DB
LABEL-$-
IN
DATA
STA
TAB
JMP
NOT A3
A5TK
C?t
* * i
JNZ
3 LANK
STA
TAB
JMP
NOT A3
BLANK
CPI
i •
JNZ
NOTAB
MV I
A f 9
; DON'
T BLOCK
FURTHER T/
1
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While these instructions will be assembled by XEK, the
CP/M will not evaluate expressions like ‘LABEL-$-l’ if the
result is negative. It seems to do OK with forward references.
Again, thanks to Mark for his inspiring program. I would
like to hear from other CP/M on Northstar users who can help
me get DDT and NRELOC working or just exchange software.
Except for the APPLE store here in Corvallis, there isn’t much
micro activity.
Sincerely, 2860 NW Skyline Drive
Gene R. Head Corvallis, Oregon 97330
THESE LINES OF TEXT HAVE BEEN MODIFIED FROM THE
ORIGINAL TEXT APPEARING IN DDJ #41, WRITTEN BY MARK
ZIEGER.
NEWLINE
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,AND SAVE IS TABCNT
Dear DDJ
Here is an observation of a serious error in programming
style that has probably been noted before, but probably not
as often or as strongly as it should have been.
First let me say that my programming style is as peculiar
in many ways as anyone’s and is certainly not beyond criti¬
cism; however, I feel that most will agree with me in regard to
this particular point.
Here is an example (can you find the problem?):
10 REM ** THIS PROGRAM IS TO POINT OUT A PROBLEM **
20 PRINT “COMPUTERS NEVER MAKE MISTAKES”
30 LET X = X + 1
40 IF X = 10 THEN 60
50 GOTO 10
60 REM ** LETS STOP PRINTING THIS JUNK **
70 END
Do you see the error? It occurs twice in the fisting. In
lines 40 and 50 there are branches to remark statements.
This may seem trivial in a small program like the one above;
however, many times it is useful to strip out remarks to save
space in a very large program. If in the above example fine 10
were deleted, the program would not run until you changed
fine 50 to ‘GOTO 20’. It is my contention that, if the prog-
grammer had done that to begin with, there would have been
no problem. It is particularly easy to make this mistake in
BASIC since every line number is potentially a label, but I
have seen examples of this in other languages also.
Sincerely, 216 Northwest Terr.
Bruce B. Thomson Silver Spring, Md. 20901
Page 58
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 45
223
Dr. DoBB'S JOURNALof
COMPUTER
(Calisthenics ^) rt hodontia
Running Light Without Over byte
Number 46 June/July 1980 Volume 5, Issue 6
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
On The Subject Of Networking
A Survey of Computer Networks 6
Art Kleiner
The Personal Computer Network (PCNET) Project: A Progress Report 10
Dave Caulkins
MCALL-C: A Communications Protocol for Personal Computers 16
Tim J.Pugh, Jr.
On Modems 22
William Smith
Random Ruminations on Networks of the Future 40
Jonathan Sachs
... and, as always, even more
225
BY ART KLEINER
Box 428
Sausalito, CA 94965
As the Information Age im¬
pends, it’s beginning to look more
and more like an interconnected
stream of computer networks. Most
networks (except for the Arpanet)
have been active three years or
less; yet already they’re having as
much impact on the people who
use them as the first automobiles
did on early drivers. Not all net¬
works are connectable to all types
of terminals, but the differences in
their design should be noted by
computer users, who are prominent
among the first computer network
memberships and influential in the
directions these networks will take.
In this survey, an update of an
article in the Summer, 1979 CoEvo-
lution Quarterly (Box 428, Sausa¬
lito, CA 94965), I tried to ask the
political questions: Who owns the
networks? Who has access to
them? How are they paid for? How
is their interaction with their mem¬
bers designed? What provisions
exist for privacy? How do people
get in touch? This is not an ex¬
haustive survey (for example, it
does not include the most influ¬
ential network of all, the Arpanet ),
but it should give some idea of
what options are available. The
two-paragraph descriptions are by
necessity over-simplified.
In meeting Dr. Dobb’s deadline,
it was not possible to fact-check all
the descriptions below. A more
comprehensive article on the sub¬
ject will appear in the Next Whole
Earth Catalog, in September 1980.
K Survey o!
Computer networks
QUBE, a two-way cable TV station
from Columbus, OH; may soon be intro¬
duced to Boston and Pittsburgh. Started
December, 1977. Sponsored by Warner
Communications Corporation and Amer¬
ican Express. Contact: Leo Murray, Vice
President of Public Affairs, 75 Rocke¬
feller Plaza, New York, NY 10019.
This widely-publicized, two-way cable
TV station offers normal cable TV, pay
TV and local channels with some inter¬
active programs. On interactive shows,
viewers push yes/no/multiple choice
buttons to respond to opinion polls or
to order products from commercials.
A central computer monitors each TV
set every 6-10 seconds, recording
responses and what channel the set is
tuned to. The system is used for political
polls, exam-taking in educational pro¬
grams, talent shows where the home
audience rates the contestants, and
commercials with built-in market re¬
search. Since American Express pur¬
chased part of Warner Communications
last year, there has been increasing
emphasis on Electronic Funds Transfer
and shopping at home.
Warner’s research showed people
wanted the simplest system possible —
hence the limited amount of interaction.
“Mrs. Jones doesn’t want to take the time
to learn to be a computer expert,”
spokesman Leo Murray said. QUBE warns
viewers in advance when their responses
are recorded, and doesn’t release records
without subscribers’ consent.
To connect you need: a TV, a $19.95
one-time installation charge, and $10.95
monthly rental. Pay-TV programs average
$1 -$4 each.
VIEWDATA is a brand name for a
type of interactive text service originally
developed by the British Insac Corpora¬
tion for the British Post Office. Like
Kleenex and Xerox, the brand name has
come to mean the entire type of product,
even though there are many competing
variations by now.
The basic British Viewdata system
involves an adapted TV set with a tele¬
phone connection and a remote control
switch box that looks like a pocket calcu¬
lator. Viewers press numbers to call for
pages of travel information, business
information, retail advertising, or
constantly updated news. News agencies
and advertisers pay the British Post Office
for the opportunity to put their messages
on the air. A central computer is signalled
through the viewer’s telephone, and
responds by finding the appropriate
Viewdata “page” and flashing it on the
viewer’s screen. Pages appear in bright
colors and block letters; each page
includes a list of 10 other pages that can
be called up for more information, like a
cross between a library and a chain letter.
(Information scientist Jacques Vallee
called it “a boring maze of branching
tunnels.”) Sometimes people must go
through seven or eight pages to find the
one they want. There is more choice than
with QUBE, but users are still limited;
they cannot communicate with each
other, except through pre-written elec¬
tronic “greeting cards.”
To connect, British viewers need an
adapted TV ($300-500 more than a
regular TV, according to one British
correspondent; $30-50 more, according
to Insac in New York) plus the price of
a phone call. Each page carries a charge,
usually 1 </-4</.
Several companies are developing
Viewdata systems in America. General
Telephone and Electronics owns the
American rights to the British Viewdata
system, through Insac Viewdata, Inc. an
American Insac subsidiary. GTE also
owns Telenet, a national network for
transmitting computer-signals cheaply,
and Sylvania, the television manufac¬
turing company. They are expected by
some observers to combine all three into
a business-oriented national Viewdata
system, which may eventually also be
adapted for home use.
The Knight -Ridder newspaper chain
is testing a Viewdata-type system called
Viewtron in Miami. Interestingly, GTE’s
major competitor, American Telephone
and Telegraph, is supplying the hardware
for this system. Contact: Viewdata
Corporation of America, One Herald
Plaza, Miami, FL 33101.
KSL-TV, Salt Lake City, and KMOX-
TV, St. Louis, both have had experimen¬
tal demonstration systems running for
two years. In both cases, a public system
is still pending FCC approval. KSL is
affiliated with the Mormon church;
KMOX is owned by the CBS Broadcasting
Page 6
226
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
Network, whose executives are reportedly
worried that viewers will switch to the
Viewdata channel during commercials.
Other Viewdata-type systems are running
ill France (Antiope) and Canada (Telidon,
with reportedly a very sophisticated
graphic “look” and animated pages.)
PCNET (Personal Computer NET-
work) is nationwide. Available from
People’s Computer Company, Box E,
Menlo Park, CA 94025.
A committee of volunteers, chaired by
Dave Caulkins of Los Altos, CA, have
developed an electronic mail system for
Commodore PET personal computers
which operates over telephone lines. Most
of the work involved developing a
method of correcting the large number of
errors caused by garbled phone-line
transmission. Users can start with PAN
programs (an illegitimate son of an
Arpanet mail system called Hermes,
Caulkins said) to send messages but need
the full PCNET program (price not
available at deadline) to transfer files and
programs without losing characters. Users
can arrange for their computer to send
the mail late at night, when they’re asleep
and the phone rates are lower.
There is no central switching computer
in PCNET. “That’s our political deci¬
sion,” Caulkins said; decentralized net¬
works are harder to control. To protect
privacy, users are encouraged to develop
automatic message-encoding programs.
Future plans include adapting other
microcomputer brands and sending mes¬
sages over short-wave radio.
PCNET has been recently joined by
similar programs doing the same for other
brands of computers. Information Un¬
limited, Inc., 793 Vicente Ave., Berkeley,
CA 94707, has developed a message sys¬
tem for Apples which they call Easy
Mover. Other programs are also being
developed — all presumably with dif¬
ferent protocols, and all unable to send
messages to any but the same program.
THE SOURCE is nationwide. Started
June, 1979. Available from Tele¬
computing Corporation of America
(TCA), 1616 Anderson Road, McLean,
VA 22101.
This was the first home-terminal
consumer information network in
America, and certainly the most am¬
bitiously promoted. People with home
terminals or personal computers can call
up specific information, including a
version of the UPI news wire and a ver¬
sion of the bibliographic New York Times
Information bank. In addition, the
Source offers electronic mail and bulletin
boards, programs which analyze statistics
off the Wall Street stock index, and a
clientele which is hungry to communicate
with eachother.
All this is transmitted over Telenet and
Tymenet, two national computer-signal
transmission networks which can be
dialed locally from most cities, and which
are much cheaper than long-distance
telephone calls. The Source intends to
market its accounts through franchised
stores called “Telecomputing Centers.”
It currently has about 4,000 active
subscribers.
According to many users, some of the
Source’s promised features — such as
airline reservation guides or conferences
— have been slow to materialize or have
not lived up to expectations. Slow
response time and frequent breakdowns
have reportedly also been perennial
problems. However, the Source deserves
credit for bringing the idea of a home-
based computer network with many more
options than Viewdata out into the open.
TCA just signed a contract with a
national library network (OCLC) to put
Source terminals in public libraries
around the country.
To protect privacy, records are kept
on the Source of how often each piece
of information is called up, but not of
who is calling for what. A directory of
users is limited to first name, state, and a
one-line description of interests — which,
ironically, cuts short the easier con¬
nection-making which a fuller direc¬
tory would provide. TCA offers a $5,000
reward to anyone who can break into the
system’s central account and access other
people’s files.
To connect, you need a terminal or
personal computer and telephone hook¬
up, a $100 entry fee (unless you buy
your terminal from the Source), and
$2.75 per hour of use. The service is
limited to off-business hours and
weekends — during business hours, it’s
$15/hour.
MICRONET was started in October,
1979. Contact: Personal Computing
Division, CompuServe Incorporated,
5000 Arlington Centre Blvd., Columbus,
OH 43220.
A home-terminal computer network,
similar to the Source, piggybacking off
the CompuServe Time-sharing company,
Micronet is younger than the Source and
concentrates on business programs, file
editing, and electronic mail. Except for a
stock price index, there are no news-wire
style databases yet; reportedly some are
planned for introduction later this year.
Micronet is more conservative in its
promises than the Source, but much
quicker in response time. A Micronet
accounts costs $9 in start-up fees and $5
for every connect hour, when signed-on
via CompuServe’s own packet-switching
network. In some cities signing on via
Tymenet is necessary, at an extra $2/
hour.
EIES (Electronic Information Ex¬
change System) is nationwide, begun
October, 1976. Originally funded by the
National Science Foundation; now
operating as an independent computer¬
ized conferencing system. Organized by
Murray Turoff and Roxanne Hiltz, co¬
authors of The Network Nation. Contact:
Anita Graziano, Computerized Confer¬
encing and Communications Center.
New Jersey Institute of Technology,
323 High Street, Newark, NJ 07102.
EIES is a community of about 900
cross-continental members, divided into
groups devoted to specific topics, such as
Technology for the Handicapped or
General Systems Theory. Many members
belong to several groups, and members
are encouraged to communicate with as
many others as they have time and
interest for. They collaborate on research,
conduct several informal news networks,
introduce themselves to each other via
keywords that signal common interests,
and gradually build up on-line libraries
of relevant information.
EIES has many members active in
community information exchange and
social alternatives; its mix of people from
corporations, government, non-profit
groups and the arts is unique among
computer networks. It’s also the site of
several specially-designed experimental
programs for weaving interactive stories
that respond to answers from the reader;
for filtering through masses of technical
information quickly; and for corres¬
ponding anonymously or under pen
names. Most EIES members sign in
through Telenet. There are about 30
European members.
To become a member, you need to
apply at the address given above.
Accounts cost $66/month and $3.75/
hour. Trial accounts are also available for
no monthly fee and $5.25/hour. Groups
can buy cooperative slots (which is true
of most networks), and can (for about
$350,000) buy the hardware, software
and maintenance to create their own
EIES-like system.
Some other computer conferencing
systems, with different mixes of member¬
ship and capabilities than EIES:
• I. P. Sharp, a less expensive system
based in Toronto, piggy-backed onto the
Sharp Timesharing network, adapted for
use by businesspeople and artists. Sharp’s
conference program is limited to one-line
comments and can be quite surreal when
five or more people are involved.
• Confer, a university-oriented con¬
ferencing network with a strong feeling
of community, based at the University
of Michigan.
• Comet, a business conferencing system,
one of the many networks developed
out of the Arpanet. Contact: Computer
Number 46
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 7
227
Corporation of America, 575 Technology
Square, Cambridge, MA 02139.
• Planet/Notepad, a relatively expen¬
sive but easy to learn business system,
managed by parapsychology investigator/
information scientist Jacques Vallee.
Planet grew out of Forum, one of the
first and most influential computerized
conferencing networks, at Menlo Park’s
Institute for the Future. For information
on Planet, contact: Sal Suniga, InfoMedia
Corporation, 530 Lytton Avenue, Palo
Alto, CA 94301.
PLATO. Started in 1969. Nationwide.
Originally developed at the University of
Illinois as a computer-aided instruction
program. Now owned and operated by
the Control Data Corporation, P. O.
Box O, Minneapolis, MN 55440.
Like Viewdata, PLATO produces its
“lessons” in pages — but unlike View¬
data, humans can interact much more
with each page, since they have a full
keyboard. Each page asks the user a ques¬
tion and produces new pages depending
on the answer. Pages compose themselves
on the screen as if the program were twid¬
dling a full-color Etch-A-Sketch behind
the scenes. Users can send messages to
anyone else on the system, although the
system does not store the messages. Up
to five conversations can go on a screen at
any one time. PLATO is used for business
training, remedial education, and training
in prison.
The public school district in Irvine,
California is developing a plan to make
PLATO available through a city-wide
cable TV system. Current plans call for a
trial system to be developed sometime
during 1980.
The specially-designed PLATO
plasma-screen terminals cost $5,000 or
more and connect time to the central
system is expensive. Most users travel to
Control Data’s own “Learning Centers”
in many cities to use the systems. The
public school district in Irvine, California
is developing a plan to make PLATO
available though a city-wide cable TV
system sometime this year.
Control Data is also beginning a pair
of computer networks for shaing infor¬
mation between small-farm farmers,
“urban problem-solvers,” and low-
income groups. These are being developed
among small groups of people now, and
have provoked controversy among some
appropriate technology and community
information advocates, who distrust
CDC’s motives. For information on
the Urban Technology Exchange, write:
Linda Jadwin, Director, Urban Tech¬
nology Exchange, HQS1 IB, Control Data
Corporation, Box O, Minneapolis, MN
55440. For the opposition point of view,
write to: Gil Friend, Office of Appro¬
priate Technology, 1530 10th Street,
Sacramento, CA 95314.
PANALOG was started December,
1977. An informal community of infor¬
mation scientists, students, and re¬
searchers in technology for the deaf,
based at General Telephone and Elec¬
tronics Labs outside Boston. Contact:
Ed Housman, GTE Laboratories, 40
Sylvan Road, Waltham, MA 02154.
Housman used excess computer time
on the GTE computer to establish his
own informal conferencing network.
Members of the network use it to discuss
information theory, plan meetings, and
generally keep up a running rap on any¬
thing of interest. Many of its members are
deaf, using it in part to keep each other
informed of news involving the deaf
community. More specifically, though,
Panalog is notable for its whimsical
human-ness (users receive three Chinese-
fortune-cookie-style epigrams when they
log off).
Five major American corporations
are expected to introduce large-scale
computer network systems for business
and possibly home use during the next
few years. They are:
1. American Telephone and Telegraph, in
addition to supplying the hardware for
Knight-Ridder’s Viewdata experiment in
Miami, AT&T is testing a terminal-in-
the-home Electronic Information Service
in Albany, New York. People use
computer terminals attached to their
phones to look up directory assistance
numbers and emergency telephone num¬
bers. In addition, there is Advanced
Communications Services (ACS), a multi¬
computer nationwide packet switching
network first proposed in 1978. ACS as
first proposed was an elaborate system
which could accept many different types
of terminals and computer hook-ups,
provide electronic mail and conferencing,
rent computer programs and store data.
AT&T has withdrawn its proposal, re¬
portedly because they hadn’t worked out
the technical bugs of such a complex sys¬
tem yet (and possibly because the regula¬
tory climate wasn’t right). There is con¬
cern among current packet-switching
networks and consumer groups that the
monopoly status and enormous assets of
AT&T would give the company an unfair
advantage over the computer network
competition.
More than any other large firm, AT&T
has shown interest in the terminal in the
home; a recent issue of a Bell employees’
magazine was devoted to the subject,
with a painting of an electronic home of
the future by Studio 54 designer Ron
Doud. Reportedly they are concerned
that involvement of many other
companies in computer networks would
lead to involvement of many other
companies in voice transmission as well.
2. General Telephone and Electronics is
developing several concurrent plans for
office-of-the-future mail and informa¬
tion systems, possibly including manu¬
facturing terminals through its Sylvania
subsidiary. GTE owns Telenet, and is
developing its own electronic mail system
on that network. It also owns the rights
to develop the British Viewdata system
in America. According to a staff member
in their Viewdata group, “We’re looking
at Business applications initially; but we
anticipate that this will evolve at some
point into a consumer system, depending
on the availability of information pro¬
viders and terminals.” Panalog was also
developed for GTE, and some of its
features may be considered for other
office-of-the-future systems.
3. Xerox, earlier this year, released plans
for two complementary computer net¬
works: Ethernet , which runs through
coaxial cables in a single building, is
already available. XTEN, which would
use its own satellites to transmit com¬
puter signals over radiofrequencies be¬
tween Ethernets, is on application before
the FCC. Like ACS, Xten would permit
many types of terminal and computer
connections; Ethernet is marketed in such
a way that connecting to it may become
a universal standard.
4. Satellite Business Systems, part-owned
by IBM Comsat, and Aetna Life In¬
surance, plans a network to transmit
computer messages and video-
conferencing between large corporate
offices over the same satellite.
5. Exxon is widely rumored to be
planning some sort of national computer
network, tied to subsidiaries which
manufacture fiber-optic transmission
lines and the laser equipment to send
messages through them. Exxon owns
subsidiaries which manufacture the Oyx
terminal; the Zilog chip; and Qwip, the
most successfully selling facsimile trans¬
mission device. Another Exxon subsidiary
is developing automatic telephone¬
answering computer systems. Reportedly,
Exxon is also developing a method for
Qwip to encode and store facsimile trans¬
missions digitally, so they could be
(eventually) tied into computer networks.
Some interesting smaller-scale com¬
puter network proposals (which don’t
exist yet):
Datacast. San Francisco, beginning
August, 1980. Formerly known as
Digicast. Proposed by Wireless Digital,
Inc., a new company managed by Jim
C. Warren, Jr., who organizes the annual
Page 8
228
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
West Coast Computer Faires. Contact:
Wireless Digital, 345 Swett Road, Wood-
side, CA 94062.
Like Teletext, Datacast will transmit
words and pictures over broadcast waves
in a steady stream. Using Sub carrier
Authorization channels, which are unused
FM frequencies linked to existing radio
stations, Datacast will be a steady stream
of wire service news, financial data, real
estate listings, classified ads, weather and
library resources. To receive it, users will
need a modified personal computer with
a radio receiver ($400 or less above the
cost of the computer). As in Teletext, the
computer will pull out only those items
which it has been programmed to catch.
Until it gets going, Datacast will be
covered in its own newsletter, available
from Wireless Digital for $5 /year.
Xanadu. Nationwide, beginning some¬
time this year. Proposed by Project
Xanadu. Contact: Theodor Nelson, Box
128, Swarthmore, PA 19081.
Nelson, who published the milestone
book Computer Lib /Dream Machines in
1972, described there his plan for a com¬
puter network system in which people
would edit alternate versions of text,
jump back and forth between the
versions, and make royalties based on
how many people would call for their
writing. His current plans call for such a
system to begin running by the end of
this year, possibly through locally
franchised “Information Centers.”
Xanadu will be used for conferencing,
writing, editing and reading. Rather than
a single index to everything on the sys¬
tem, users will be encouraged to create
their own indexes to what interests them
and publish them for others.
Nelson said they are looking at hourly
costs of $2 (300 baud) and $5 (1200
baud). Xanadu may operate its own trans¬
mission hardware instead of relying on
Telenet or Tymenet; or the Xanadu sys¬
tems may only operate locally.
The Community Memory Project, San
Francisco, is beginning sometime this
year. Sponsored by the Community
Memory Project. Contact: Sandy
Emerson, 916 Parker Street, Berkeley,
CA 94710.
Convinced that computer networks
should be decentralized, open to
everyone and service-oriented, Com¬
munity Memory put inter-connected
terminals in Berkeley public places
between 1973 and 1975. People used the
system as an electronic bulletin board for
news, messages, classified ads and poetry.
Others used the terminals to pull out
information with the appropriate key¬
words, or to add comments to existing
messages. A new similar system will be
established in a Bay Area neighborhood.
Up to 20 terminals will be placed in
community centers and neighborhood
gathering places. All information in the
system will be entered by the people
who use it, and no one will connect to
Community Memory through private
terminals. In the meantime, some of the
text editing and file-arranging programs
which will compose the Community
Memory system are being offered for sale
separately.
OCLC/Home Delivery of Library
Services is starting mid-1980 in
Columbus, OH at first; then possibly
nationwide. Contact: Philip Schreiber,
OCLC Inc., 1125 Kinnear Road,
Columbus, OH 43212.
OCLC used to be the Ohio College
Library Center. Their new home system
will use a keypad like QUBE’s (but smaller
and less expensive), an adapted TV, and
the telephone lines. Columbus residents
will use OCLC’s system to bank at home
and to call up pages of an on-line
encyclopedia. OCLC is also planning to
put Source terminals in libraries nation¬
wide.
AIM is an EIES-like conferencing sys¬
tem, with an emphasis on developing
a community computer system for
alternative communities. Contact: Steve
Heitmann, Rt. 2, Box 502A, Portland,
OR 97231.
Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
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THE PERSDnflL CdiTlPUTER nETWDRR
[PCflET] PROJECT:
A PROGRESS REPORT
BY DAVE CAULKINS
PCNET Project
1263 El Camino Real, Box E
Menlo Park, CA 94025
INTRODUCTION
This article describes the PCNET
project, its goals, a brief history of ac¬
tivity, PCNET status today, and PCNET’s
future plans.
GOALS
The goal of the PCNET project is to
provide a reliable, error free and low-
cost means of transferring files, programs
or messages among personal computers
(PCs) via the dial-up telephone system
or other media. To achieve this goal in
a reasonable way the PCNET Project
adopted a series of system design objec¬
tives:
1. PCNET software will be hardware-
and operating-system independent; any
PCNET-equipped computer will be able
to communicate with any other PCNET-
equipped computer.
2. PCNET will be adaptable to as broad
a range of existing hardware and software
systems as possible.
3. PCNET will be a distributed system;
any two computers running PCNET
software will be able to communicate
with no requirement for additional
centralized resources. However, this will
not preclude time-sharing systems and
other centralized services from running
PCNET ‘front ends’ in order to communi¬
cate with PCNET equipped small com¬
puters.
4. PCNET will be capable of unattended
operation; any two PCNET systems will
be able to initiate a telephone connection,
transfer information and terminate the
connection without the presence of an
operator at either end. This will allow
PCNET systems to take advantage of the
low telephone rates available from
11 PM to 8 AM.
5. No personal computer user will require
more than a single telephone line to
participate in PCNET.
6. PCNET will be layered; i.e., PCNET
software will be divided into distinct
functional layers. Communication be¬
tween layers will be sparse and well
defined. Any layer can be modified or
even replaced with minimum effect on
the others. This kind of design should
make PCNET readily adaptable to chang¬
ing opportunities in hardware and media.
Modems are going to be capable of higher
speeds, and communication by other
media such as radio (see discussion of
Packet Radio below) will become pos¬
sible. Layering allows relatively easy
accommodation to these technological
advances.
PCNET History
The PCNET Project (then called the
PCNET Committee) was started at the
first West Coast Computer Faire in
April of 1977. PCNET was and is a non¬
profit organization of volunteers; all
PCNET developed software is placed
in the public domain. PCNET is now part
of People’s Computer Company. The
first year of PCNET activity produced a
protocol design (a protocol is a set of
conventions for computer-to-computer
telecommunication) and some experi¬
mental software mechanizing protocol
operation. This software was demonstra¬
ted at the second Faire in March of 1978;
an 8080 based system in Santa Clara,
CA sent a file to a PET at the Faire in
San Jose, CA with both machines run¬
ning PCNET software. Noise was delib¬
erately introduced on the phone line to
damage some blocks of data; the two
machines successfully detected the bad
blocks and retransmitted good ones.
In 1979 the TNW Corporation and
PCNET developed PAN, a small electro¬
nic mail system. This sytem lacks the
power of the full PCNET protocol,
but is quite adequate for handling English
text messages and allows people with
limited telecommunications experience
to get a feel for what telecommunication
is all about. The first version of PAN
runs in the Commodore PET and TNW488
modem; a program tape and instruction
manual are available from P.C.C. for $12.
We’re working on a version for the Apple
II and Micromodem II, and intend to
do one for the TRS-80. See Appendices
B and C for more information about PAN.
PCNET STATUS
PCNET Design Description. This sec¬
tion presents a brief description of
PCNET design. Each PCNET installation
is called a Node;it consists of a computer,
a modem, and the PCNET software.
The software will activate one of two
capability levels: Simple, for machines
of small size or limited resources, and
Advanced, for more powerful machines.
A 48K Apple II with a Micromodem II
is an example of a machine which could
become an Advanced node. In keeping
with PCNET design objectives all nodes
will be able to communicate in Simple
mode, but two nodes able to switch to
Advanced mode will be able to do more
and do it faster. Node-to-node communi¬
cation always starts in Simple mode,
but switches to Advanced mode as soon
as possible if both nodes can handle it.
Figure 1 shows a diagram of the
PCNET layers as they are implemented
in hardware and software in a PCNET
node. The node that initiates a call
(dials the phone) is called the originate
node; the node that accepts a call (an¬
swers the phone) is called the answer
node. Information starts at the top
(server process) layer of the originate
node, works its way down through the
layers and across the phone line to the
answer node. There it goes back up
through the answer node layers to the
server processes. At the top (server)
layer in both nodes area the programs
actually carrying out user functions—
for example a File Transfer Program
(FTP), an electronic mail program
(MAILER), etc. PCNET can communi¬
cate data to and from several simulta¬
neously active server programs.
Let’s follow the sequence of events
in detail, assuming that both FPT and
MAILER are active, and that the phone
connection to the answer node system
has already been established. Starting
at the top (server) layer in the originate
node: each server process passes a stream
of data to the Directing layer; MAILER
is sending an electronic mail message,
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
and FTP is sending an object program
to be executed later in the answer node
computer.
Directing Layer. In this layer the two
streams of data are broken up into
Directed Blocks; each such block has a
header with the address of the server
process in the answer node to which it’s
to be delivered, and a data section con¬
taining a piece of actual data. The Direc¬
ted Blocks are then passed to the Valida¬
ting Layer.
Validating Layer. Here the Directed
Blocks have additional header informa¬
tion added, and an error detecting code
appended to the end of each block.
The resulting Validated Blocks are
passed to the Translating Layer.
Translating Layer. In this layer the
Validated Blocks undergo a translating
process; they are converted into Radix-
41 format if this is a Simple node, or
into transparent binary if this is an
Advanced node.
Radix-41: Radix-41 is a 2 byte to a
3 character packing scheme invented by
Mike Wilber; the conversion from binary
to Radix-41 guarantees that no control
characters appear in the transmitted
data which might cause undesired actions
by some operating systems. Thus use of
Radix-41 guarantees that PCNET will
run without interference under any op¬
erating system known to us. Either
Radix-41 or transparent binary can
handle data in binary, ASCII or any
other form, but transparent binary
supports higher transmission speeds.
Framing Layer. Here the Translated
Blocks have delimiting characters added,
resulting in Framed Blocks.
Hardware Layer. This layer consists of
the modem and any other hardware
required to interface to the dial-up
telephone system. Modems suitable for
PCNET use are under full software con¬
trol; a detailed discussion of modems
may be found in Appendix A. In the
modem the bytes making up the Framed
Blocks are translated into serial bits,
each of which is then converted into
one of two audio tones for transmission
over the phone line.
Now let’s follow the information as it
goes through the same layers in the op¬
posite direction in the answer node.
Hardware Layer. The answer node modem
converts the sequence of audio tones
into a serial bit stream, and this is turned
into a sequence of Framed Blocks.
Framing Layer. Here the framing char¬
acters are used to identify the block
starting points; they are then discarded
resulting in Translated Blocks.
Translating Layer. In this layer the
blocks are translated into binary; from
Radix-41 if the nodes are operating in
Simple mode, or from transparent binary
if they are in Advanced mode.
Validating Layer. The error detecting
codes in each block are evaluated; if the
block is error-free an acknowledgement
block is created and sent to the ori¬
ginating node, indicating to it that the
current block has been successfully
received and that the next block may be
transmitted. The error detecting code and
Validated Block header material are
stripped from the block, and the re¬
sulting Directed Block is passed up to the
next layer.
Directing Layer. The header of the block
is examined to see whether it is intended
for the FTP or MAILER process in the
answer node; all remaining header ma¬
terial is stripped off and the data is passed
to the indicated process.
PRESENT PCNET ACTIVITIES
A small group of PCNET people is
presently (April, 1980) working in¬
tensively to develop 1 to 4 complete
implementations of the PCNET protocol
running in several different computer/
modem pairs. The resulting software
will be in the public domain; it will be
distributed to anyone at modest cost and
will probably be published here in DDJ.
This software is also intended to serve as
‘model’ software in a PCNET im¬
plementation workshop to be held
later in the year. We hope this work¬
shop will produce many additional im¬
plementations covering the majority of
computer/modem pairs in use today.
All this software will support real but
sparse Server level processes such as
file transfer and electronic mail.
A volunteer organization like PCNET
is not well suited to creating and main¬
taining software products. It’s our hope
that individuals and software companies
will use PCNET software as the basis
for products which will utilize PCNET
protocols as a telecommunication stan¬
dard.
FUTURE PLANS
Although the dial telephone network
is easily accessed, it is far from ideal
as a PCNET medium, since it is op¬
timized for voice and not data. Phone
system bandwidth is limited and costs
are high and going higher. We believe that
radio offers both lower cost and higher
bandwidth. US Government research has
shown that many PCNET type users can
effectively share a single radio frequency
allocation using a technique called packet
radio. The Canadian Government has
wisely assigned radio spectrum space
(220-225 MHz) for Canadian radio a-
mateurs to experiment with packet
radio. We’d very much like to start
similar experiments in this country.
Canadian experience indicates that the
entire radio transceiver and interface
could be built for about $500, a price
which would decline with any kind of
production volume. Some reports by
CARF (Canadian Amateur Radio Fed¬
eration) on packet radio work in Canada
are reproduced in Appendix D.
The PCNET project would like to see
packet radio administered under licensing
much more similar to CB radio than
to amateur radio. We think packet radio
equipment can be designed to prevent
abusive behavior by ill-informed or mali¬
cious users.
APPENDIX A
PCNET Modems
All telephone based data communication
systems require modems to function. The
features required for a PCNET modem are as
follows:
Hardware Features
-Receive sensitivity of at least -40dBm;
-45 to -50 dBm preferred
— 10 pole receive filter; 6 pole transmit filter
— 300 baud operation
Features Under Software Control
— Answer/originate mode select
— Switch hook control; pulse dialing
—Carrier detection
-Incoming ring signal detection
Desirable But Not Necessary Features
-FCC Part 68 registration, permitting direct
connection to the phone line without an
otherwise legally required Data Access
Arrangement
-Telephone signalling tone discrimination,
allowing software to detect DIAL TONE,
BUSY, CALLED PARTY RING, etc.
-Software selectable baud rate
-Power up on incoming ring detect.
The PCNET Project has found a
number of modems that are suitable for
PCNET use. A list of them is given below:
TYPE — SI 00 Compatible
The MM —103, from Potomac Micro-Magic,
Inc., First Lincolnia Bldg, Suite Bl, 4810
Beauregard St., Alexandria, VA 22312.
Costs $359.95; is FCC Part 68 certified.
The Micromodem-100, from D.C. Hayes
Number 46
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
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Associates, Inc., 16 Perimeter Park Dr., Suite
101, PO Box 9884, Atlanta, GA 30319.
Costs $350.00; is FCC Part 68 certified.
The 88-MODEM, from International Data
Systems, Inc., 400 N. Washington St., Suite
200, FaUsChurch, VA 22046. Costs $395.00
TYPE — Apple Compatible
The Micromodem II, from D. C. Hayes (see
address above). Costs $389.00; is FCC Part
68 certified
TYPE — PET Compatible
The TNW488, from The TNW Corpora¬
tion, 5924 Quiet Slope Drive, San Diego,
CA 92120. Costs $320.00
APPENDIX B
PAN SOFTWARE
Just recently, the PCNET Project an¬
nounced the availability of computer mail
support software for use on personal com¬
puters. The software is called PAN, named for
the illegitimate son of Hermes, the messenger
of the Gods in Greek Mythology. The PAN
software, in fact, was inspired by a sophisti¬
cated mail system called HERMES which was
developed by Bolt, Beranek and Newman,
Inc., for the DEC System 10 and System 20
computers.
PAN is a completely self-contained com¬
puter system. Any two PAN systems can
exchange messages over an ordinary voice
telephone line. PAN allows entry, review and
automatic transmission of messages at times
selected by the user. When a message is sent
to a PAN it automatically answers the phone,
receives and stores the message, and hangs up
the phone to wait for the next incoming or
outgoing message. Similarly when PAN has a
message to be sent it automatically picks up
the phone, dials the number of the recipient
PAN, verifies that carrier is present and that
PAN is active, transmits the message, and hangs
up the phone to wait for the next transaction.
Message exchange is possible between any
two PAN systems regardless of the type of
computer or modem used. Either or both PANs
can record both incoming and outgoing mes¬
sages on tape or disk.
PAN is the result of a collaboration between
The Personal Computer NETwork (PCNET)
Project of PCC and TNW Corporation. PAN is
similar to Community Bulletin Board Systems
(CBBS) in general functioning and command
structure. It is different in that PAN is a dis¬
tributed system; there is no single phone
number and set of equipment through which
all messages must pass.
The PAN system has communications ad¬
vantages over Jjoth traditional mail and the
telephone, and cost advantages over existing,
expensive electronic mail systems.
Advantages of PAN over traditional mail;
• Immediacy of delivery (or if preferred,
“time tag” delivery)
• A signal from the receiving computer
allows the sending computer to mark
the message “sent.”
Advantages of PAN over telephone communi¬
cation:
• PAN can record all received and trans¬
mitted messages for future reference
• The PAN user need not be present to
transmit or receive information
• The PAN system has a “keep trying”
feature which will wait until the line
is clear to deliver the message.
Cost Advantages over existing electronic mail
systems:
• Low entry cost
• PAN uses the dial-up telephone network
• Telephone charges can be quite low
• PAN software is available for a cost of
$12, including manual
• PAN runs on a personal computer.
The present PAN system is best for letter
(English language) communications. PAN is
designed so that all existing computer terminals
now in use in major universities and corpora¬
tions can access PAN systems to read and write
messages. Terminal-to-PAN communication is
primitive due to the limited capacities of
existing terminals.
The PCNET Project plans continued de¬
velopments following this initial version of
PAN. Some of these are detailed here:
• Improvements in the error management
capabilities of PAN. At present the error
rate of PAN messages is about 1 error for
every 5 minutes of message transmission.
This error rate is not adequate for computer
programs or financial data. An error rate of
1 error for every two weeks of message
transmission appears to be attainable.
• A file transfer capability will be sup¬
plied. This will allow a complete pro¬
gram to be sent from one personal com¬
puter to another over the telephone.
Because of the low error rate the receiver of
the program can be confident that the
program will run successfully. This file
transfer capability will allow ‘bootstrap’
loading of the PCNET program itself over
the phone. To do this, a very short program
is loaded by hand into the computer. This
short program then manages the transfer of
the much longer PCNET program from a
remote computer via the phone line. By this
process the PCNET programs can migrate
from computer to computer very easily.
• The PCNET Project hopes to experiment
with other than the telephone system as
the communication link between PCNET
computers. One possibility is radio which
has the potential of markedly increasing
the amount of data that can be transferred
while decreasing the cost.
PAN Commands
E — Enter a message. The phone num¬
ber of the PAN for which the
message is intended must be in the
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Number 46
first line of the message. After
message entry the user can select
a mode assignment for the message.
I — Immediate; send this message now.
D — Deferred; hold this message for
transmission later. The user is
prompted for the time of trans¬
mission.
N — Make no mode assignment for this
message. A mode can be assigned
later as described below.
Q — Query; hold this message for sub¬
sequent retrieval by a non-PAN
modem equipped computer or
terminal.
M - Mode assignment. Assign a new
mode to the message whose number
is given by the user.
R - Retrieve a message. The message
whose number is given by the user
is displayed.
S — Summarize messages. The numbers,
modes and initial portions of all
messages in the buffer are displayed.
K — Kill (erase) the message whose
number is given by the user.
U — Unload PAN, restore operating
system pointers and write an end-
of-file on the message record tape
or disk.
? -- List the PAN commands.
Modem equipped terminals or com¬
puters can send a message to a PAN
system by calling the PAN and sending a
special control character before the mes¬
sage text. A second control character
after the text causes PAN to store the
message and hang up the phone.
PAN has been implemented for the
Commodore PET and TNW488 modem;
we are working on a version for the
Apple II and Hayes Micromodem II.
We plan versions for the TRS-80, S-100
systems, etc.
To receive the current PAN package
(a cassette tape of the PET
version of PAN and a user’s manual)
sign and send the enclosed PAN license
agreement with a check for $12 to:
PCNET Project, People’s Computer Com¬
pany, 1263 El Camino Real, Box E,
Menlo Park, CA 94025. Please also
include the size of your PET’s
memory — 8K, 16K, etc.
We’re distributing PAN under a li¬
cense agreement for a number of reasons:
• We want to be sure that all versions of PAN
will be able to talk to one another.
• We want to provide a central organization
for the roster of PAN users, and for the
distribution of new PAN versions.
• We want to protect the rights of TNW Cor¬
poration, our associate in the PAN de¬
velopment program.
APPENDIX C
PAN Lower Level Protocol
1. The originating PAN dials the number of
the answering PAN.
2. When the answering PAN detects ring, it
goes off the hook and sends carrier.
3. When the originating PAN detects carrier
it sends carrier.
4. When the answering PAN detects carrier
it sends the string “@@@ANN” where ANN
consists of a single alpha character followed
by two numerics. This string is the version
number of the answering PAN; as of 6 Feb
80 it is P09.
5. When the originating PAN receives one or
characters it sends 5 CTRL-S characters.
6. When the answering PAN receives one or
more CTRL-S characters it prepares to accept
subsequent received characters as a PAN
message. If no CTRL-S characters are received
the answering PAN times out and goes on hook.
7. The originating PAN sends the message
text. The first line of this text (between the
first character and the first carriage return)
contains the phone number of the originating
PAN in the form (AAA)NNN-NNNN. By
convention this first line also contains the
sender’s initials and the originate PAN local
time of transmission in 24 hour format; HHMM
SS where HH ranges from 00 to 23.
8. The originating PAN sends 4 CTRL-R
characters to signal end of message; it then
goes on hook.
9. When the answering PAN receives one or
more CTRL-R characters it goes on hook
and places the received character string in the
message buffer. If the answering PAN loses
carrier at any time during message reception it
goes on hook.
APPENDIX D
Packet Radio in Montreal
This report about packet radio was pre¬
pared by Canadian Amateur Radio Federation,
Inc. To be put on their mailing list, which
means you will receive their next four Packet
Radio Newsletters, send $5 to Art Blick at
CARF, P.O. Box 356, Kingston, Ontario
K7L 4W2. The money is to defray the costs
of reproduction.
Since the Montreal group was the first
into packet it is not unusual that this group
is the furthest advanced in this technology.
A system has been fully operational since
August of 1979, and has been continually up¬
dated since then. There are currently six
stations on the net, with more working on
modems and computers right now.
The net operates on 223.5 MHZ cur¬
rently, but a move to 222.3 is expected as
soon as all of the stations have their crystals.
Audio frequency shift keying is used, at 2400
bits per second. The mark tone is 2400 HZ
and space is 4400 HZ. The modem is based
on the Exar 2206. 2211 chip set, with a credit
to Ted Balesta VE3CAF who first suggested
the design. Having experimented with the
design for almost a year now, it is capable of
error-free transmission with S/N ratios of
15 DB or so. Its perfection is due to the efforts
of Jacques Orsali VE2EHP who “massaged”
the design to its present performance levels.
The radio is typically the Midland 13-509,
running ten watts. It was chosen on the virtue
of simplicity and price. The modificiations to
it are simple and can be done in about thirty
minutes or so. The interface to the radio was
deliberately kept as simple as possible in
anticipation of future users who may be either
unwilling or unable to make extensive mods
to the radio. Since just recently, Ted VE3CAF
has joined the Montreal team, and we expect
that he will make substantial improvements to
the interface.
The local net is being used for man-to¬
man communications mostly, but lately the em¬
phasis has switched to machine-to-machine
transfers of programs, text files and the like.
One user is currently writing a multi-user
real time war game which will be implemented
on the net soon. One of the unresolved ques¬
tions is what major use the net will be put to
once fully implemented. Since this will depend
on the character of the users, it will stay a
question for some time yet.
The network includes a store and forward
repeater as part of the system, and this repeater
is currently functioning. It was demonstrated
at the RSO convention in the fall of 1979.
It receives packets which are flagged as packets
for repeating, and rebroadcasts them a few
miliseconds later. It serves the same purpose
as a conventional 2 meter job, i.e., it extends
the range of a station using it. Since there are
no cavities (it is a simplex device) it does not
suffer from the usual problems of desense,
and split antennas. Naturally, it is very ef¬
ficient and as we say in the business, “it talks
far.”
The repeater operates on the same fre¬
quency as the rest of the net and only re¬
peats pacs which are flagged to it. In this way
we find two stations often using the repeater
while two others who are close enough use
simplex, all on the same frequency. In addition
to its conventional roll, Digptr as it is called,
offers other services to the users. By sending
a pac to it (as opposed to through it) users
can get a “Broadcast Message” which provides
important information of immediate interest,
system shutdowns, protocol changes and the
like. The message can be changed remotely by
the system operators, and is password pro¬
tected. Users can also use the Digptr to check
out their system. Using the Test facility, a
packet sent to Digptr, will be transmitted back
to the station the same way it was received,
that is, with or without errors. By accessing the
status file of the repeater, users can see the
number of pacs, and acks which have gone
through Digptr, as well as those which were
“direct” and bypassed it. System operators
can use this function for statistics on usage,
and throughput.
The latest and perhaps most exciting de¬
velopment is that we now have a single board
computer/terminal working. It is based on the
Motorola Chroma II kit, sometimes called
the TV BUG. This low cost ($300 or so) de¬
vice will implement the full packet protocol
in PROM, and requires only a keyboard, a
TV set and a compatible modem to run. This
means that the cost of a complete packet set¬
up is reduced by a factor of about ten. We
figure about $500 including the radio would
be the maximum cost for someone who had
nothing to start with. For those people who
have micro computers already, TV bug will
(continued on page 58)
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Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
MCALL-C: A Communications Protocol
for Personal Computers
BY TIM J. PUGH, JR.
Micro-Call Services
9655-M Homestead Court
Laurel, MD 20810
In the protocol description which follows, I will identify
alternative approaches that were considered in arriving at the
present protocol. But before getting into the protocol itself
I would like to try to clear up a misunderstanding that may
exist concerning telecommunications protocols. The type of
protocol which I am describing has no bearing on the informa¬
tion content of the data. The protocol acts simply as an en¬
velope or container of data. The data is inserted into the
envelope at the originating (transmitting) end and auto¬
matically removed at the receiving end. Thus, by the time the
data is placed on disk, it looks exactly the same as it did on
the disk of the originator.
Perhaps the first question to answer is “why have a proto¬
col?” The principal reason for having one is to insure, as far
as possible, that no data is lost or garbled in the transmission.
One can, and I often do, transmit and/or receive data files
with a large Time Sharing Computer (TSC). These TSCs
are typically very uncooperative beasts which output the
data to you in “their own good time,” usually as fast as it
can be sent. They are not concerned about whether you had
noise on the line or whether you had time to write the last
record to disk. That’s your problem. Thus, if you have a
system which pays rapt attention to the incoming data and if
the weather is good and you have a high quality modem, then
you have an excellent chance of receiving error-free data.
However, one cannot depend on all the above stated
conditions being met, especially when two personal computers
are involved. Such a transfer will frequently be “long dis¬
tance.” Each additional TELCO switching center involved in
the “call” reduces the signal-to-noise ratio and often there is
line “echo” distortion present. Thus, reliable data transfer
becomes questionable without an intervening mechanism. An
appropriate communications protocol supplies this mecha¬
nism.
Serial Versus Blocked Data Format
The simplest way to transfer a file is the way it is done with
a TSC. The file is simply transferred serially to completion.
It is assumed the receiving file has already been created
and that the TSC is capable of recording the data at the
maximum BAUD rate; e.g., 300 BAUD. Such an approach
can also be used for transfers between two Personal Com¬
puters (PCs) provided the operation is properly coordinated
Copyright© 1980 by Tim J. Pugh, Jr.
Page 16
234
and synchronized. However, it is preferable to have the two
computers do the necessary synchronization and coordination
since it is then both more convenient for the users and less
error prone. We have thus posited a protocol whereby the file
is automatically opened at the Transmitting (TX) end and
created at the receiving (RX) end and might look something
like this:
—@SOH < Cfilename> <Ctyp>
<— (SACK
—> <file data>
The directed arrows indicate the direction of data transfer
where “—>” indicates data from the TX to the RX. The
signifies ASCII and thus @SOH indicates the ASCII
Start Of Header control character. Similarly, “@ACK” signi¬
fies ASCII ACKnowledge. Assuming that the originating
(TX) operator has previously specified the name of the file
to be transferred; i.e., <filename><type> and further
assuming that communication has been established between
the two parties, then the transfer is initiated by the TX end
issuing an @SOH followed by the name of the file. Since an
indeterminate amount of time is required for the RX system
to create the corresponding file, and ACKnowledgement is re¬
quired before the data transfer can begin. Why an indetermi¬
nate amount of time to open a file? Partly because there is
such a variety of floppy disks and controllers capable of run¬
ning under CP/M (both 8” and 5 &”). Since a “handshake”
character, @ACK, was required to signify “file created OK”;
why not include the option of sending @NAK (Negative Ac-
Knowledge) to signify some problem in opening the file?
Let’s further assume that if @NAK is received by the TX
end, the “@SOH <filename><typ>” will be repeated.
Since we have provided for retransmission (reTX) of the
Header Record, the next question is: how can we discontinue
the retransmission, assuming the problem persists over several
reTXs? This introduces a third control character, @CAN
(ASCII CANcell). Thus our “handshake” in response to the
Header Record can take one of three forms. This situation is
handled nicely by the BACKUS-NAUR notation which fol¬
lows:
<ack. form> : : =@ACK I @NAK I @CAN
which states that the acknowledge form is defined equal to
either @ACK or <®NAK or @CAN.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
We next look at the <file data>. The most conventional
method for “recording” received data is to first buffer it in
memory and subsequently write it to disk. This allows the RX
system to handle high BAUD rates, e.g., 1200 BAUD, without
data loss. However, if large files are transferred, buffer over¬
flow might result. Thus, it is desirable to allow the buffer to
be “dumped” to disk at appropriate times. A simple solution
to this problem is to break the <file data> into small blocks
followed by an <ack. formX Thus, if the data is broken into
equal blocks of 128 characters the protocol would look some¬
thing like this:
—> @SOH <filename> <typ>
<— @ACK
—> <data.blk>
<— @ACK
—> <data.blk>
<— @ACK
— > <Cdata.blk>
<— (SACK
The @ACK following each <data.blk> tells the TX system
that the buffer write operation is complete and the next
block can be sent. The above considerations argue strongly
for a BLOCKED rather than a SERIAL data format for our
protocol.
Data Integrity Considerations
The blocked protocol specified thus far provides for error
recovery (reTX) in the event the <filename><typ> was
garbled; e.g., noise caused a given character to be converted
to a characger which is not legal when specifying file names.
It also provided time for data blocks to be transferred from
memory to disk. However, no provision has been made to in¬
sure that data integrity is maintained.
The most commonly-employed technique for handling this
problem is to use either a Cyclic Redundancy Check (CRC)
or a Checksum. The CRC usually employs a polynomial
equation for its realization. The term checksum, as used
here, simply means a sum of all the characters in a given
data block. Since each character in the ASCII set can be
represented by seven data bits, this simply means the accumu¬
lated total obtained by adding each character in turn, to the
previous partial sum. I have chosen the checksum because of
its simplicity and ease of implementation.
In implementing the checksum, two choices must be
made: (1) The block size over which the checksum is to be
taken; (2) The number of bits to be allocated to the checksum.
The most convenient block size appears to be that associated
with one physical record on disk; i.e., a disk sector of 128
bytes. Having chosen the first parameter we find that the
largest value the checksum could take on occurs if the ASCII
rubout character (@DEL = 07FH) is repreated 128 times.
Since 07FH is equivalent to 127 decimal, the worst case
checksum would be:
SUM = 128 * 127 = 16256
This value falls between 2 A 15 and 2 A 16. Thus, a 16 bit
checksum would insure a unique sum for each unique data
block. I am using the term “unique” rather loosely here.
Two data blocks consisting of the same characters but in
different order are not considered unique, by this definition.
At least one popular “serial I/O” card employs a UART
whose output is fixed at 7 data bits. The Cromemco TU-ART
employs the Texas Instruments TMS5501 device to support
serial I/O. The serial output of this device is fixed at 7 data
bits with a parity bit of zero. Thus, while it would be most
efficient to transfer the 16 bit checksum as two eight-bit
characters, this approach would exclude systems employing
the TU-ART card to drive an acoustic coupler. For this
reason, an ASCII HEX encoding of the checksum was em¬
ployed. This results in the 16 bit value being broken into
for “nibbles” of 4 bits each. The ASCII representation of
each nibble ranges from ASCII 0 through 9 and ASCII A
through F. There remains the question of ordering the output
value; i.e., what sequence should be used in transferring the
nibbles. I somewhat arbitrarily chose the most significant
nibble first and least significant nibble last.
We now nave a protocol where each data block, including
the header block, has a checksum associated with it. As each
character is transferred, both the TX and RX systems accumu¬
late individual checksums. The TX system transfers its final
value to the RX, who tests it for equality with its own value.
If the values agree, an @ACK is returned, otherwise a @NAK
is returned and the data block is retransmitted. How many
times should reTX be allowed to occur on the same data
block before cancelling (@CAN) the transfer? I have somewhat
arbitrarily chosen the value of 5. Remember, it takes quite a
bit of time to repeat a data block 5 times. Five repeats plus
the original at 300 BAUD requires approximately:
retry time = 6 * (128 + 4) /30 Sec. = 26.4 Sec.
Also remember we are not dealing with “crud” on a disk
(which uses 10 retries) but with noise on the line. If the line
noise, or perhaps some system problem, causes a reTX in ex¬
cess of 5 times on the same data block, brother, you have a
problem! Note further that many more than 5 reTXs are
allowed provided no more than 5 occur on a given data block.
While we seem to have solved the data integrity question on
a data block basis, we still need some way of assuring ourselves
that each and every block was received properly and that
some reTXed block didn’t get recorded twice by mistake. One
approach is to include a block or frame count as part of the
block transfer. Since the files transferred might be quite
large, a 16 bit block count might be needed. Given the 7 data
bit limit mentioned above, this would require an additional
4 characters per block. I chose a different approach which
does not add to the size of the data block. I have found that
if a cummulative total of reTXs is kept by both TX and RX
systems, then the equality of these values virtually assures
the transfer was error free. Thus, the TX system sends his retry
count to RX system as a part of the End of TeXt (@ETX)
record. This record immediately follows the last <data.blk>
record. If the counts agree, the RX system sends @ACK.
Else, a @NAK is sent. Both systems then display on their
respective consoles that the transfer was either successful
or unsuccessful along with the total number of reTXs.
We now have a protocol that looks something like the
following:
—> @SOH FILENAMETYP SUM
<— @ACK
—> AAAAAAAAAAAAAAAA SUM
<— @ACK
—> BBBBBBBBBBBBBBBB SUM
—> JJJJJJJJJJJJJJJJ SUM
Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 17
235
<— @NAK
—> JJJJJJJJJJJJJJJJ
<— @ACK
—> KKKKKKKKKKKKKKKK
<— @ACK
(Retransmission Request)
SUM
SUM
—> ZZZZZZZZZZZZZZZZ SUM
<— @ACK
—> @ETX CNT
<— @ACK
The “SUM” associated with each data block represents the
four ASCII HEX characters associated with the checksum. The
“CNT” at the end represents a single character value inter¬
preted as a binary retransmission count value. Thus, it repre¬
sents the count modulo 128 since the number of data bits in
the protocol is set to 7 data bits.
Variable Block Size and Data Parity Check
The above protocol is about as far as we can go if limited to
7 data bits and no parity. However, since most UARTS/
USARTS provide for both software control of the number of
data bits (5 thru 8) and additional control over parity selection
(even or odd) coupled with parity enable/disable, valuable
additions can be made to the protocol.
Let’s first consider variable block size. If we limit the block
size to one sector (128 characters) then we must access and
write the disk every 4 seconds (approx.) at 300 BAUD. The
read/write head on most drives unloads within this interval.
Thus, the head is being loaded each time a write operation is
performed. This takes on the order of 36 Msec or about one
character time at 300 BAUD (33.3 Msec per character). In
addition, the proper sector must be found — assuming the
head is already positioned at the appropriate track. Since it
takes 166.6 Msec for one rotation of the disk, the average
“latency” is one half that value; i.e., 83.3 Msec. Thus, each
time we write the disk costs us, on average,
retransmission request due to parity error, two additions to
our protocol are needed. First, we must add a resync (@SYN)
request to our <ack. form>. In response to the receipt of s.n
@SYN from the RX device, the TX device will discontinue
the block transfer and begin a retransmission of the same
block. Second, to assure proper synchronization, each data
block should begin with a Separator (@RS) for this task.
Thus, if the RX device detects an @RS following his trans¬
mission of an @SYN, he knows the block retransmission
request has been received by the TX device and that this is
the beginning of that block.
Finally, it is desirable to be able to identify a block with
more or less characters than specified by the block count.
This can be done by inserting a special character between the
end of data and the beginning of the checksum. I have se¬
lected the ASCII Unit Separator (@US) for this task. If there
is such a disagreement, a @SYN is immediately sent by the
RX to the TX, causing a retransmission. This completes the
protocol specification and leaves us with a typical data block
that looks something like,
—> @RS N XXXXXXXXXXXXXXXXXXXXX @USSUM
<— @ACK
where N denotes the block count and, as before, SUM denotes
the checksum.
I have given this protocol the name “MCALL-C”, which
stands for Micro proto “CALL”-Clear. The clear means that
the data is not encoded, as is the case for the PCNET proto¬
col. In PCNET protocol, the data is encoded in a radix 41
code rather than pure ASCII. This encoding allows binary
information to be transferred while using only 41 “printable”
characters to encode the data.
The complete MCALL—C definition both in BACKUS-
NAUR form and in a more graphic form (section (3) ) is
shown in Table 1. The definition is from the point of view
of the originator or (TX) system.
write time = 83.3 + 35 Msec = 118.3 Msec.
This is approximately 4 character times at 300 BAUD and
16 character times at 1200 BAUD. The worst case time would
be approximately 211.6 Msec or approximately 6 character
times at 300BAUD (includes 10 Msec track stepping time).
These times apply to the Stugart 800 drive. The times should
be fairly representative of all floppy disk drives.
Given the above statistics, it seems desirable to increase
the block size and thereby reduce the number of times a disk
write operation is performed. In arriving at an optimum block
size (if one exists) we must consider the impact of increased
block size on both buffer memory size and time lost in retrans¬
mitting a larger data block. I have no firm number in mind
but since CP/M allocates disk space in 8 sector blocks, a value
of 1024 = 8 * 128 seems a good starting point. This calls
for a 16 bit block size value which can be sent as two 8 bit
bytes interpreted as binary values rather than ASCII char¬
acters. To be consistent with the checksum ordering the most
significant byte is transmitted first.
The next protocol enhancement to be introduced provides
for a parity error test. If a data parity error is found, there is
no need to continue the block transfer. Instead, the block
should be immediately retransmitted. This further facilitates
the introduction of larger block sizes. To accommodate the
<1> DATA TRANSMITTED (BXXX SIGNIFIES AN ASCII CONTROL CHAR)
<FILE> <F.HDR> <F.TEX>
<F.HDR> :■ BSOH <HEADER> (PUS <CHKSUM>
<HEAOER> * <8 CHAR FILENAME> <3 CHAR FILETYPE>
<CHKSUM> - <16 BIT CHECKSUM ENCODED IN ASCII HEX
MS-NIB8LE FIRST, LS-NIBBLE LAST)
<F. TEX> « <TEXT) (PETX <ERRTTL>
<TEXT> - <BLOCK> I <BLOCK> <TEXT>
<BLOCK> = (PRS <CHRCNT> <STRING> (PUS <CHKSUM>
<CHRCNT> = <NUMBER (LESS ONE) OF CHARACTERS IN <STRING»
<STRING> :■ <PRINTABLE ASCII CHAR STRING OF FILE DATA)
<ERRTTL) * <TOTAL ERROR COUNT MOO 128)
(2) DATA RECEIVED (HANOSHAKING PROTOCOL)
<ACK. FORM) = <BACK) I «PNAK) I <(PSVN) I «PCAN>
<(PACK> = (PACK (SUCESSFUL TRANSFER OF DATA)
«?NAK) = BNAK (RETRANSMISSION REQUEST)
<(?SYN) - (PSYN (RESVNC REQUEST)
<(?CAN) = BCAN (ABORT TRANSMISSION)
<HDR.ACK): = <F.HDR) <ACK.FORM)
<BLK.ACK) = <BLOCK) <ACK.FORM)
CEOF.ACK) - (PETX <ERRTTL> <ACK. FORM) (FILE CLOSED ACK)
(3) SAMPLE FILE TRANSMISSION
—> BSOH FILENAMETYP (PUS SUM
<— BACK
—> (PRS N AAAAA. . . AAAAA (PUS SUM
<— (PACK
—> (PRS N BBBB8. . . BBBBB BUS SUM
<— BACK
—>
(PRS N VVVVV. .
.VVVVV
BUS
SUM
<—
BNAK
(RETRANSMISSION REQ)
—>
(PRS N VVVVV. .
. VWW
BUS
SUM
<--
(PACK
--)
(PRS N YYYYY. .
.YYYYY
BUS
SUM
<—
(PACK
—)
(PRS N ZZZ2Z. .
.ZZZZZ
BUS
SUM
<—
(PACK
—>
(PETX M
(END OF FILE)
<—
(PACK
(HEADER BLOCK)
(FIRST DATA BLOCK)
(SECOND DATA BLOCK)
Page 18
236
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
Having specified the protocol, we must now resolve the
problem presented by the existance of UARTS whose number
of data bits is limited to seven and whose operation does not
support parity generation and testing. The best approach
might be to have two similar but different protocols. One to
accommodate the TMS5501 and another to take advantage
of the 8 data bits plus parity. Let’s call the 7 bit version
MCALL-C and the 8 bit version, MCALL-BC. The “B”
related to the Big data block size. The two protocols are
identical except in the way the block size and the checksum
are represented and the use of parity testing in one but not
the other. By limiting the differences to these three para¬
meters, both protocols can be accommodated by the same
program. A “flag” could be set in response to operator input
to specify which processing path was selected.
For MCALL-C we define the block size and the checksum
as follows:
<CHARCNT> : : = <NUMBER (LESS ONE) OF CHARACTERS
IN <STRING>IN THE RANGE 0 TO 127>
<CHKSUM> : : = <16 BIT CHECKSUM ENCODED IN ASCII
HEX WITH MS-NIBBLE FIRST>
For MCALL-BC we define these two parameters as follows:
<CHARCNT> : : = OJUMBER (LESS ONE) OF CHARACTERS
IN <STRING> IN THE RANGE 0 TO
65535 with MS-BYTE FIRST>
<tHKSUM> : : = <16 BIT CHECKSUM WITH MS-BYTE
FIRST>
As to the effectiveness of the protocol, I have implemented
the MCALL-C protocol as part of a program I have written
called “MCALL”. The program fixes the UART data format
at 7 data bits with even parity, although no parity test is
currently performed. This protocol has been tested on a
vaiety of I/O cars for the S-100 BUS and includes the Cro-
memco TU-ART. I find the protocol very effective in file
transfers and have never had an unsuccessful transfer under
normal circumstances. By normal I mean under both good and
foul weather conditions with total reTX counts ranging
up to 10 or more per message. I generally get error-free
performance even when I tap on the telephone handset with a
pencil to introduce noise. Occasionally, however, using the
“bang approach” I have caused the system to “bomb” or
record the same block twice. However, the operator is alerted
to the latter case via an “unsuccessful file transfer” message
at the end. This is where the comparison of reTX counts
pays off.
The current version of MCALL (VI.6) supports only
MCALL-C. I hope to add MCALL-BC in the future, along
with other protocols and program enhancements. Further
information relating to MCALL can be obtained by con¬
tacting the author whose address is given at the beginning of
tliis article.
UPDATE NOTICE
February 22,1980
The following changes to MCALL VI.5 will remove a po¬
tential problem which exists when sending a file to a remote
TSC at 300 BAUD. When a TSC becomes “loaded” and its
response time deteriorates, it is possible to lose some of the
file data being sent. It is usually the case that, while a TSC
may not be capable of receiving continuous data at 300 BAUD,
it is capable of handling this rate for the duration of a single
line. The proposed change to the file TX routine causes the
transfer to pause at the end of each line and await acknow¬
ledgement in the form of a line-feed. Further, the remote
device is allowed to follow this @LF with additional characters
(e.g., a prompt character) before transmission of the next
line commences.
The proposed change results in a new version number,
MCALL VI.6. The following directions should be followed in
order to implement the change:
1. Change the second line of the source file to reflect the new
version number, VI.6. Search for the unique string “MSG1:”
and change the second line of that message to reflect the
new version number.
2. Either perform a negative search or revert to the start of
the source file and search for the unique string “KONSW:”.
On the next line, insert the following storage declaration:
IDLCNT: DS 2 ;IDLE LINE COUNTER
3. Search for the unique string “TF3:” and then advance 5
lines. At that point, replace the statement “CALL SHOW”
with the following:
MOV C, A
BIOSS CONOUT ;CRT <- CHAR
This will cause the CRT to display only the printable
characters during a TX file operation, rather than converting
non-printing control characters to their printing equivalent.
While this change has nothing to do with the stated problem,
it seems a desirable change.
4. Search for the unique string “TFEOL:” and advance 6
lines. Kill this and the next 5 lines; i.e., the LDA, ORA, JNZ,
MVI, CALL, and JMP instructions. Now, advance to the end
of the subroutine and kill the last instruction; i.e., the “JMP
TXBYTE” instruction. In place of this last instruction, the
following instructions should be appended to the subroutine:
AN I
07FH
CPI
OLF
JNZ
TF4
;LINE ACKNOWLEDGED 7
TF4B
LX I
H, 8
i YES
SHLD
IDLCNT
,IOLCNT <- 0
,--WAIT FOR
LINE TO GO
IDLE
TF5.
LHLD
IDLCNT
I NX
H
SHLD
IDLCNT
;♦+IDLCNT
MOV
A/ H
AN I
03H
> TEST ONLY 10 LS8S OF COUNT
ORA
L
JZ
TXBYTE
iIS LINE IDLE?
CALL
MSTAT
j MAYBE NOT
AN 1 '
RDA
JZ
TF5A
i RX DATA AVAILABLE?
IN
RXDATA
J YES
AN I
07FH
MOV
C, A
BIOS*
CONOUT
>CRT <- CHAR
LDA
•CHCNT
I NR
A
STA
CHCNT
.++CHCNT
JMP
TF4B
; RESET IDLE COUNT AND WAIT AGAIN
TF5A
BIOS*
CONSTS
JZ
TF5
,CONSOLE DATA AVAILABLE
JMP
TFEND
J YES, TERMINATE FILE TX
Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 19
237
That’s it. Sorry this change was not included in the VI.5
update but an earlier attempt to resolve this problem in
assembly language failed. It was not until I recently re-coded
the program in the language “C” that I was able to resolve
it. It’s fairly trivial, once you see the solution. Oh well, that’s
the way it goes.
For those of you who want the update but would prefer
to receive it on disk, I will apply the same “deal” as before.
Return the old disk and receive an update for $5. Otherwise,
send $10. and I will ship you the update on a new disk.
As far as I know, this is the last of the significant changes
that the program requires. However, I will keep you informed
of any “bells & whistles” that may be added in the future.
UPDATE NOTICE
April 8,1980
This update is principally aimed at the “ESC F” function.
This update will change the version number from VI.6 to
VI.7. In VI.6, the filename and filetype were specified on
separate lines and lower case characters were not converted to
upper case, as required by CP/M (sorry ‘bout that). Also, it
was not possible to specify a file as residing on other than the
“logged in” disk. This update corrects these problems.
The first thing that must be changed is the version number
appearing on the first “page” of the source. It also appears
following the unique string “MSG1:”. Next, search for the
unique string “MSG20:” and replace this message with the
following message:
MSG20: DB CR, LF, ’ENTER <FILENAME> .<TYP>-DISK
SPEC (e.g. B:) ’
DB ’OPTIONAL’, CR, LF, LF, ’$’
. —KKUUfcS>S> <-r 1 Lfc-WintI rrc/
PRINT* MSG20, * - REQUEST <FILENAME> & <FILETYPE> FROM OPERATOR
MVI C,ROCBUF
LX I 0, C BUFF
CALL FDOS ; GET <IFILENAME>. <TYP>
;—PROCESS OPTIMAL DISK SPECIFICATION
LOA
CBTXT+1
CPI
» : *
JN2
FILES
> OISK SPECIFIED?
LDA
CBTXT
; YES
AN I
3
STA
FCBON
; FCBON <- DISK_SELECT
LDA
CBCNT
OCR
A
OCR
A
;CBCNT = CBCNT - 2
LX I
H,CBTXT+2
JMP
FILE4
, —MOVE
<FILENAME> * <TVPE> TO FCB
FILE3
LOA
CBCNT
;A.REG <- CHAR CNT
LX I
H.CBTXT
, H, L.REG <- SOURCE ADDR
FILE4:
LX I
D, FCBFN
;D- E.REG <- DEST_ADOR
CPI
13
JC
FILES
, CHAR CNT > 12?
MV I
A, 12
; YES
FILES
CALL
MOVCAPS
;FCB O FILE NAME, TVP
CALL
CRLF
RET
; *♦ *******************************************************************
, «
MOVCAPS
— Move
a block of characters from source to destinatio
l
and
convert to upper case <CAPS). Also, screen
*
out
*. * if found.
/
A.REG = count
i
H, L.
*EG = source_address
>
D. E.
REG = dest_address
; —— *******************************************************************
MOVCAPS
MOV
B, A
ORA
A
MOVC1
R2
>MOVE COMPLETED?
MOV
A, M
; NO, GET A CHAR
CPI
•
JN2
MOVC 2
, CHAR = ». »?
I NX
H
i YES
LX I
0. FCBFT
,0, E.REG <- FCBFT
DCR
B
JMP
MOVC 1
GET THE NEXT ONE
MOVC 2
CPI
061H
JC
M0VC3
,LOWER CASE CHAR?
AN I
0SFH
, YES, CONVERT TO UPPER CASE
M0VC3:
STAX
0
.MOVE TO DESTINATION
I NX
H
I NX
0
OCR
B
JMP
MOVC 1
Enclosed is a two page listing of the new subroutines
required to implement the change. These two routines replace
the single previous routine named “FILE.” Thus, it will be
necessary to search for the unique string “FILE:” and replace
the existing routine with the two attached routines. Note that
the old and new FILE routines are identical through the three
lines following the line labeled “FILE2: ”.
One last minor change fills the final sector of a “recorded”
disk file with 01 AH. This assures that no “garbage” is present
in the last record of a recorded file. Only one line of code
need be changed. To do so, search for the unique string
“BB2D3:”. Advance to the next line and change the symbolic
jump address from “BB2D5” to “BB2D4”. That’s it. Simply
change the ’5’ to a ’4’ and reassemble. Enjoy!
; * + ********************* ****** ********************** *** ***************
> * * FILE — File Control Block setup
i Provide for operator selection of a new file by
i prompting him for his selecti-on and then set up
; the associated F.C.B.
i
;— *******************************************************************
FILE:
MV I
B, 33
MV I
A, 0
LX I
H, FCB
; — 2ER0
FILL
THE ENTIRE
FCB
FI LEI
MOV
M, A
I NX
H
DCR
B
JN2
FI LEI
; FCB 2ER0ED?
.—BLANK FILL
<FILENAME>
& <FILETVPE>
MV I
B, 11
; YES
MV I
A, • *
LX I
H, FCBFN
FILE2
MOV
M, A
I NX
H
DCR
B
JN2
FILE2
. BLANK FILL COMPLETE?
Page 20
238
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
THE ELECTRIC PHONE
A Directory of 144 Computerized
Bulletin Board Systems
BOOK
A computerized bulletin board works
just like an ordinary bulletin board
system except that instead of paper and
thumbtacks it uses a terminal, a computer,
and the dial-up telephone network.
It’s a place to leave messages for every¬
one or for some particular person who,
you know, browses the bulletin board
occasionally.
The list below was developed from
several sources including the Peripheral
People in Mercer Island, Washington
and the People’s Message System in San¬
tee, California. It is being maintained
by PCC’s PCNET project, our effort to
bring computers and telecommunications
into the hands of everyone. While this is
the most complete listing we have as of
this writing, we would appreciate addi¬
tions and corrections. Send them to
PCNET, PCC, P.O. Box E, Menlo Park,
CA 94025 or leave them on the PCNET/
PCC Bulletin Board System for Dave
Caulkins, (415) 948-1474.
All the bulletin board systems listed
here can be accessed by telephone using
a 300-baud ASCII terminal and a Bell
103 modem. Most use carriage-return as
a speed recognition character, after which
they are self-teaching. All are free to
anyone who calls, unlike the Arpanet,
which is restricted, and The Source and
MicroNet which cost money. The list
has been sorted by area code; consult
your local telephone directory for geo¬
graphical correspondence.
We are compiling a mailing list of people
interested in computers and telecom¬
munication. If you would like to be
on it, send us a note at the address
above. If you are interested in PAN,
PCNET’s computer mail system for the
PET, send us a stamped, self-addressed
envelope and we’ll send you back
information.
1
(201 )
457-0893
( 213 )
795-3788
( 314 )
838-7784
( 604 )
687-2640
( 714 )
—
730-1206
m
jal
( 201 )
835-7228
( 213 )
799-1632
( 316 )
746-2078
( 607 )
754-5571
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Page 21
239
Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
ON modems
BY WILLIAM SMITH
2325 >2 Howe Street
Berkeley, CA 94705
Micronet ID: 70110,243
Source No: TCD650
Like all new areas that emerge in this
world of microcomputers, the area of
phone line connection is fraught with
unclear terminology and generalities. I
spent much energy sorting things out
in order to set myself up ‘on line’ and
would like to share some of what
I have learned with you. To begin, some
terms must be defined:
MODEM a general term that can refer
to any of several different aspects of the
physical device which couples a computer
to the phone lines.
ACOUSTIC COUPLER a specific type
of modem that makes an acoustic connec¬
tion between the computer and the
phone lines by setting the phone hand¬
set into a cradle which is connected to
the computer.
DIRECT COUPLER another specific
type of modem that makes a direct
connection between the computer and
the phone lines; everything stays in the
form of electric signals; there are no
intermediary acoustic stages.
MODULATOR/DEMODULATOR the
circuitry responsible for encoding and
decoding information represented by
logic states (i.e., high and low) to and
from information represented by vibra¬
tion rates (i.e., high frequency and low
frequency).
FREQUENCY SHIFT KEYED (FSK)
jargon for the frequency coding tech¬
nique typically used in modems (and
many cassette interfaces); a sine wave is
the carrier of the binary information and
the data is stored by shifting the fre¬
quency to one value for a high and to
another value for a low.
BANDWIDTH a continuous region or
band of frequencies defined by the differ¬
ence between two specific frequencies
which denote its upper and lower limit,
e.g., the bandwidth of FM radio is ap¬
proximately 20 Mhz, from 88 Mhz to
108Mhz.
A data communcations link-up is a
two way connection. Both parties can
send and receive information. This is
facilitated by dividing the phone line’s
available bandwidth into two separate
bands or channels. Each one of these
corresponds to one of the two different
directions in which data is being sent.
There is a 450 hz band in the IK region
and another 450 hz band in the 2K
region. Within each of these 450 hz
regions we need to distinguish to separ¬
ate frequencies, corresponding to the
two logic states that must be represented.
The logic states are coded in FSK mode.
Thus each state requires only a few
hertz bandwidth. The separation between
the logic one frequency and the logic
zero frequency in both the upper and
lower regions is 200 hz. Refer to the
table for a graphic representation of all
this information. The exact figures for
the upper and lower bands representing
the two communication directions may
vary between manufacturers according to
filter design but the four logic levels are
precisely defined industry standards.
This is necessary if machine independent
communication is going to take place.
If one of the two communication chan¬
nels, say the upper one, were reserved
for the send direction of communication,
and the other were reserved for the re¬
ceive direction, then consider the pro¬
blems that would ensue. Both parties
would be sending their messages on
the send channel and expecting to hear
from the other on the receive channel
where there would be silence! Clearly
there has to be a more definitive agree¬
ment about who is the sender and who is
the receiver.
The solution lies in defining a new
term: Mode. When two parties are in
communication, the one that placed the
call is considered to be in Originate Mode
and the other is in Receive Mode. In
Originate Mode the upper communication
region is your receive band and the lower
region is your transmit band. In Answer
Mode the two are reversed. Thus if A
calls B then A is in Originate Mode and
will transmit on the lower region, while
B will be in Answer Mode and therefore
receiving A’s transmission on the lower
band. On the upper band B will be trans¬
mitting and A will be receiving.
The major difference between an acous¬
tic coupler and a direct coupler computer
phone link up is the element of personal
presence. In the acoustic coupled situa¬
tion someone must be there to physically
dial the phone and set the handset on the
coupler; or, in the Answer Mode, wait
till the phone rings and then make the
physical connection. With the direct
coupler the computer remains plugged
directly into the phone lines and, via a
combination of software and hardware,
is responsible for all functions including
answering a ringing phone, dialing num¬
bers, dealing with broken connections,
checking for data errors and just about
as many other technical details that the
programmer wants to get involved in.
The direct coupled situation also
tends to suffer less from loss of data
problems due to the fact that it does
not have any intermediary acoustic
stages. Furthermore, with a direct
coupled arrangement, a microcomputer
owner is able to access his/her machine
from any remote location; e.g., your
computer is at the office and you have a
Page 22
240
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
relatively inexpensive terminal at home
giving you the full power of your com¬
puter at home. Acoustic couplers cost
about $150 while the direct couplers
seem to hover around the $400 mark.
In the final analysis, I chose the direct
coupled equipment because I have a
vision of starting a small local network
for sharing resources and ideas in the
Berkeley, California area. I feel that it
is the responsibility of the people who
own computers now to break into the
new territory of Networks and thus pre¬
vent the concept from becoming solely
connected with major nationwide com¬
panies. Local computer networks could
revolutionize just about every aspect
of our lives, giving people in communi¬
ties a true and present sense of being in
touch with one another.
Any persons mterested in pursuing
this topic should get in touch either by
phone, mail or Micronet Bulletin Board.
•••••••••••••••••••••••••A*
Let me leave you with a final question,
! readers; if anyone knows the answer,
please get in touch with me: How can
data be traveling in two directions at the
same time on one line, and how does the
phone company send our voices two
ways at the same time without having
separate bands, since our voices use
| up the whole band? — WS
(•••••••••••••••••••••••••a*
Page 24
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
241
ADDING ARRAYS TO FORTH
BY RALPH DEANE
Box 27
Little Fort, B.C., Canada VOE 2C0
In some versions of FORTH (notably FIGFORTH) there
are no functions which can be used to define multidimen-
sioned arrays. Other versions (those based on the Caltech
manual) provide only a primitive array defining function. The
power of FORTH is such, however, that these array-defining
functions can be added with relative ease. This extendability
of the compiler to add new classes of functions (in this case
arrays) is shared by few other languages and is one of the
strengths of FORTH. Functions to define one, two, three, and
four dimensioned arrays will be presented here. Careful study
of the program will show the underlying principles, which can
also be applied to arrays with five or more dimensions.
In FORTH there are two different methods of defining
functions whose purpose will be to define arrays. One way
is to use ;CODE while the other is to use (BUILDS DOES).
;CODE produces the fastest runtime speed when generating
addresses of array elements but is also processor-dependent
due to its use of assembler language. While (BUILDS DOES)
may be slower than ;CODE, all parts of the definition are in
high level FORTH, which makes it processor-independent
and allows the functions produced to be transportable. This is
the main reason that (BUILD DOES) will be used in the
function definitions. All true implementations of FORTH
should have these functions available. If your version does not,
find out why from the distributor. Programma International’s
FORTH does not have these functions and is, in any case,
not a true implementation of FORTH, as defined by the
FORTH interest group.
The defining functions are organized such that the func¬
tions they produce will return the absolute address of the
desired array element. The indices of the element must be
placed on the stack before executing the function. All indices
have a lower value of 1. No error checking is provided to test
for indices out of bounds.
In order to understand how the defining functions work,
a knowledge of how (BUILDS DOES) works is required.
An explanation of this is beyond the scope of this article and
should be covered in your FORTH manual. Each of the four
defining functions works in the same way.
The defining function can be broken down into two parts,
compile time and runtime. The compile time portion is execu¬
ted when an array is created. It consists of the code from
(BUILDS to DOES). It gets the size of each dimension, stores
them in the dictionary and then reserves the required words
for the array storage area. Figure 1 shows the order in which
the dimension sizes are stored for each array type. The amount
of space reserved is equal to the product of all the dimension
sizes.
Dimension 1 is X
Dimension 2 is Y
Dimension 3 is Z
Dimension 4 is W
1 Dimension Arrays
first parameter field - X
2 Dimension Arrays
first parameter field —
second X
3 Dimension Arrays
first parameter field -
second
third
4 Dimension Arrays
first parameter field —
second
third
fourth
Figure 1 .
The runtime is executed whenever the address of an array
element is required. It expects the address of the first para¬
meter field to be on the top of the stack, with the indices
underneath it. The index of the highest dimension is closest
to the top. The formulas used to compute the element addres¬
ses are outlined in Figure 2.
FPF is the address of the first parameter field. X, Y,
Z, W are the dimensions of the array. I, J, K, Lare the
indices of the element.
1 Dimension Arrays
I * 2 + FPF
2 Dimension Arrays
((((I—1)*Y) + J + 1)*2) + FPF
3 Dimension Arrays
(((( I - 1) * Y) +J + 1) * 2) + (X * Y * (K - 1)) +2 + FPF
4 Dimension Arrays
((((I - 1) * Y) + J + 1) * 2) + (X * Y *Z * (L— I)) + 4 + FPF
Figure 2.
Number 46
242
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 25
EXAMPLES
1 Dimensioned Arrays
50 1ARRAY PUT - define an array of length 50 called PUT
to get the address of’PUT [ 11 ] execute 11 PUT
2 Dimensioned Arrays
ROM BYTE - FINDER FOR
THE APPLE II
BY STEPHEN E. BACH
Route 2, Box 50A-1
Scottsville, VA 24590
5 7 2ARRAY NAME — define a 5 X 7 array called NAME
to get the address of NAME [3,4] execute 3 4 NAME
3 Dimensioned Arrays
5 6 7 3ARRAY DIM — define a 5 X 6 X 7 array called
DIM to get the address of DIM [1,5,2] execute 15 2 DIM
4 Dimensioned Arrays
2 3 4 5 4ARRAY NAX - define a 2X3X4X5 array
called NAX
to get the address of NAX[ 1, 3, 2, 4] execute 1 3 2 4 NAX
The version of FORTH used to develop these functions is
called 6502 FORTH. There are a few differences in function
names between it and FIGFORTH. These are:
6502 FORTH FIGFORTH
I
SAVE >R
UNSAVE R>
For more information on 6502 FORTH for the KIM-1
and the Sym contact Eric Rehnke, #61 — 540 Ranch view
Circle, Anaheim Hills, CA 92807.
0 < SCR #01 )
1 i 1 ARRAY <BUILDS DUP # 0 DO 0 * LOOP DOES>
2 < RUNTIME ROUTINE ) SWAP 2 * ♦ I
3 i MAT ROT 1 - SWAP DUP • ROT * ROT ♦ 1 ♦ 2 • ♦ l
A * 2ARRAY <BUILDS OVER OVER ' ' • 0 DO 0 ' LOOP DOES>
5 < RUNTIME ROUTINE ) MAT t
6 I 2MAT DUP DUP t SAVE 2 ♦ • SAVE SAVE ROT ROT UN SAVE MAT
7 SWAP 1 - UNSAVE * UNSAVE • 2 • ♦ 2 ♦ 1
13 t 3ARRAY < BUILDS SAVE OVER OVER # # UN SAVE DUP # * *
M DO 0 ' LOOP DOES>
10 ( RUNTIME ROUTINE ) 2MAT I
11 l 3MAT SWAP SAVE DUP SAVE 2MAT 2 ♦ INSAVE DUP t SWAP DUP
12 2 ♦ • SWAP 4 ♦ • * * IN SAVE 1 - * 2 * ♦ t
13 * 4ARRAY <BUILDS SAVE SAVE OVER OVER # # UN SAVE DUP '
14 UNSAVE DUP ' • * • 0 DO 0 ' LOOP DOES>
115 ( RUNTIME ROUTINE ) 3MAT I
In the Sept/Nov 1977 issue of KIM User Notes, Hal
Gordon, long-time friend of DDJ, noted that the 6502 BIT
instruction can be used to non-destructively test the accumu¬
lator for any possible bit combination. The BIT instruction
performs a logical AND on the byte in the accumulator and
a mask byte. The mask byte must be addressable because the
BIT instruction has no immediate addressing mode. Hal then
presented a table of addresses in the KIM’s ROM at which
there were specified hex values in the range $00-FF; the
KIM’s ROM contained 175 of them.
The enclosed routine for the APPLE II will find such
values in the Apple’s Integer Basic/Monitor ROM beginning
at $E000. The Apple’s ROM contains all 256 values. The
program stops after the screen has filled with addresses and
their corresponding values to allow you to copy them if you,
like the, do not have a printer. Pressing any key will start the
program on its way again.
Credit should also go to Lee Moyer, who helped.
ROM BYTE-FINDER
FOR
APPLE
11
0800
A9
00
LDA
#00
Initialize registers to zero:
0802
85
00
iSTA
00
Byte-to-be-found
0804
85
01
ST A
01
Addresses-prlnted counter
0806
85
FE
STA
FE
Low byte of ROM's beginning address
0808
A9
£0
LDA
#E0
high byte of ROM's beginning address
080A
85
FF
STA
FF
080C
A0
00
LDY
#00
080E
B1
FE
LDA
IFE).Y
Load byte from ROM
0810
C5
00
CMP
00
Is It the one we're looking for ?
0812
DO
28
BNE
083C
If not go to examine next byte
0814
20
DA
FD
JSR
FDD A
Print byte found
0817
A9
A0
LDA
#A0
Print space
0819
20
ED
FD
JSR
FDED
081C
98
TYA
Move low order byte of ROM address
081D
AA
TAX
to X register for printing
081E
A5
FF
LDA
FF
Load hi order byte of ROM address
0820
20
41
F9
JSR
F941
Print address of byte found
0823
20
48
F9
JSR
F948
Print 3 spaces
0826
E6
01
INC
01
Bump addresses-prlnted counter
0828
A5
01
LDA
01
Test for full screen
082A
C9
5C
CMP
#5C
Full screen Is 92 addresses
082C
F0
05
BEQ
0833
If full go wait for key to be pressed
082E
E6
00
INC
00
Bump byte-to-be-found-reglster
0830
DO
D6
BNE
0808
If more bytes to find go do It
0832
60
RTS
That's all; return to monitor
0833
20
35
FD
JSR
FD35
Go watch keyboard for key-down
0836
A9
00
LDA
#00
Reset addresses-prlnted counter
0838
85
01
STA
01
083A
F0
F2
BEQ
082E
Go to resume search for next byte
083C
C8
INY
Bump Index to examine next ROM byte
083D
F0
02
BEQ
0841
If page boundary bump hi addr of ROM
083F
DO
CD
BNE
080E
Go to examine next ROM byte
0841
F.6
FF
INC
FF
Bump hi byte of ROM addr
0843
DO
C9
BNE
080E
Go to examine next ROM byte
0800
A9
00
85
00
85
01
85
FE
A9
E0
85
FF
A0
00
B1
PE
0810
C5
00
DO
28
20
DA
FD A9
A0
20
ED
FD 98
AA
A5
FF
0820
20
41
F9
20
48
F9
E6
01
A5
01
C9
5C
F0
05
E6
00
0830
DO
W
60
20
35
FD
A9
00
85
01
F0
F2
C8
F0
02
DO
0840
CD
E6
FF
DO
C9
Checksum = 42 704
Page 26
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
243
BY DONALD E. KNUTH
Computer Science Department
Stanford University
Stanford, California 94305
Herewith a portion of Donald Knuth’s collected errata for
The Art of Computer Programming. Future issues of DDJ
will contain more collected errata. — SR
This report lists all corrections and changes of Volumes 1
and 3 of The Art of Computer Programming , as of January 5,
1979. This updates the previous list in report CS551, May
1976. The second edition of Volume 2 has been delayed
two years due to the fact that it was completely revised
and put in the TEX typesetting language; since publication
of this new edition is not far off, no changes to Volume 2
are listed here.
throughout the book(s)
The present report was prepared with a typesetting system
that is now obsolete; please do not wince at the typography.
All changes and corrections henceforth will be noted in TEX
form on file ERRATA. TEX [ART, DEK] at SU-AI.
In spite of inflation, the rewards to error-detectors are
still $2 for “new” mistakes in the second edition, $1 in the
first edition.
Please do not endanger the author’s morale by asking him
about Volume 4. Thank you for your understanding.
The preparation of this report was supported in pajt by
National Science Foundation grant MCS-77-23728, by
Office of Naval Research contract N00014-76-C-0330, and
by IBM Corporation.
2128178 2
when the text of these books is on a computer I will try to be consistent in hyphenating
compound adjectives like doubly-linked lists and storage-allocation algorithms, etc. ... but
until then, such lapses are not to be considered errors
line 11
Leibnitz Leibniz
line -7
5127178 2
11129/77 4
the theorem that the theorem
line 16
11129/77 5
3,...
3.
line 3, under the big pi
11112176 6
n,
n
Number 46 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Page 27
244
ll/iil1 displayed formula in exercise 32
2/25/75 7
Page 28
n/ c ■''V+ n/c
QJx 1*2 add a footnote (see p. v for style)
4119177 8
line 3 after (1): book. •'‘V* book.'*'
footnote for bottom of page: In fact, permutations are so important, Vaughan Pratt has
suggested calling them "perms." As soon as Pratt’s convention is established, textbooks of
computer science will be somewhat shorter (and perhaps less expensive).
lines -4, -5(twice), -7, -15, -16 11112176 9
••• ...
lines 3, 10, 11, 12, 21 11112/76 10
••• •'V* . ..
£L,£HI exercise 21 line 1 7/31/76 11
Faa Faa
line 13 2/25/75 12
manner ''"V* matter
line 6 after Table 1 5/25/76 13
Szu-yuen Szu-yuan
change in Eq. ( 17) 11/12/76 14
-r r and r 'V -r
Eq. (18) 7/31/76 15
n > 0. •'V* n.
line after (19) 11/12/76 16
-r r
caption to Table 2, replace third line by: 9/21/76 17
see D. E. Barton, F. N. David, and M. Merrington, Biomotrika 47 (1960), 439-445; 60
(1963), 169-176.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 46
245
£,^2 line -4
11115178 18
Number 46
246
n n(k-l) ^ ^»i-l)(fc-l)
lines 8,9,10 6/25/76 19
Kepler, ... life. A* Johann Kepler, 1611, who was musing about the numbers he saw
around him [J. Kepler, The Six-Cornered Snowflake (Oxford: Clarendon Press, 1966), p.
21 ],
£„0§ line -7 11/29/77 20
use same style script F in this line as in line -6 (six places)
£JE new generalized Eq. (29) 8/25/76 21
(*/(•*-1))" - 1 - (1/(|.-1))[“_ 1 > 4 (1/(i.-1)(«-2))["_2> 2 - • • • - l m B k M i k /kl (29)
(convert this to usual format for displayed equations)
update to previous correction number 25 11/12/76 22
to appear, A^» 75-77,
£,$£ replace lines 1-3 by the following new copy 8/25/76 25
The coefficients which appear in the last formula are called "generalised Bernoulli
numbers"; Section 1.2.11.2 examines them further in the important special case n ■ 1. For
small k, we have Bj^^/kl * (-D^tJJ.fc] (n-/c-1 )!/(n-1)!, but when k > n this formula breaks
down since it reduces to 0 times oo. An analogous situation holds for the power series
(a/lnO+z)) rt , where the coefficient of e k for k < n is {”_^}(n-fe-l)!/(n-l)l.
£,^2 line -8 7/51/76 24
Faa A^* Faa
£caption, line 2 7/51/76 25
2.11 A/* 2.10
£,£0§ line 3 7/51/76 26
Faa A^ Faa
£,££0 three lines after (12) 6/25/76 27
*m ^ l« m l
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 29
£,£££ line 8
11115178 28
Page 30
mately 2 mately (-l)^ + ^^2
line -6
Analysis ■'V* A crude analysis
HjHIKs) line -6 and Eq. (22)
n n- l/2 n n
Q&QV line 5
three •'“V* two
£L„Hfi£3 exercise 5
n n_ l/2 n n
UdiSS line 2
is loaded. 'V* are loaded.
line 1
The contents A portion of the contents
line 7
is ■"‘V* are
11129/77 29
11/29/77 80
11/29/77 81
11/29/77 82
1/16/77 88
1/16/77 84
1/16/77 85
line-19 11/15/78 86
Overflow may occur as in ADD. * / 'v* Same as ADD but with -V in place of V.
lines-18 through-13 11/15/78 87
move this paragraph in front of the SUB definition on the preceding two lines
line-12 4/19/77 88
flUL requires ■'N/ 4 HUL, NUfl, CHAR each require
QJ&WV box 05 4/19/77 89
1 V 10
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 46
247
lines -10,-9,-8
4119177 40
CON 'V* CON (4 times)
£,,£22 line 16 11129/77 41
facilate • / V* facilitate
stylistic corrections 6/14/77 42
line 2: i.e. ■N' 4 e.g.
line 3: (X ^ (Here X
line 5: sun. ■'"V* sun;
line 10: (E • / Ss* (This number E
line 22: the year that the year
lines 19-21 6/14/77 45
An illustration...See also the book See, for example, the book
Q'SZffl line-11 6/14/77 44
F - 7 F - 9
line -9 6/25/76 45
about 1946 **V* during 1946 and 1947
£,213^ line -10 12/19/76 46
down an item •'V* an item down
up the stack •'‘V* the stack up
insert new paragraph after line 4 4/19/77 47
Further study of Algorithm C has been made by D. S. Wise and D. C. Watson, BIT 16
(1976), 442-450.
line 4 9/21/76 48
we exercise 30 describes a somewhat more natural alternative, and we
new exercise 9/21/76 49
30. [17] Suppose that queues are represented as in (12), but with an empty queue
represented by F * A and R undefined. What insertion and deletion procedures should
replace (14) and (17)?
Number 46 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 9402S
248
Page 31
JOSSES exercise 9 line 4
girls A* women
5/ 2/77
50
line 8 4119/77 51
otherwise. A^* otherwise, making the latter node the right son of NODE (Q).
new quote to insert just before Section 2.3.2 1/16/77 5 2
Binary or dichotomous systems, although regulated by a principle,
are among the most artiTicial arrangements that have ever been
invented.
—WILLIAM SWAINSON, A Treatise on the Geography and ClassiTication of
Animals, Sec. 250 <1835)
line 13 6/25/76 55
In all A^» Furthermore TYPE (U) is set appropriately, depending on *. In all
line 2
12/19/76 54
there is a man now living having A* somebody now living has
line -1
with ■''V* than
line -2
as A/* informally as
line 11
-types A* -tuples
5/27/78 55
1/16/77 56
5/27/78 57
QtWis) line 18 11/15/78 58
Polya A/* Polya
step A2 lines 2-4 2/28/78 5 9
unmarked, mark it, and if A/* unmarked: mark it and, if (twice)
lines 14-15 9/21/76 60
[See the ... 372.] A/* An elaborate system which does this, and which also includes a
mechanism for postponing operations on reference counts in order to achieve further
efficiency, has been described by L P. Deutsch and D. G. Bobrow in CACM 19 (1976),
522-526.
Page 32 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
249
line 17 77/29/77 61
see A/-* see N. E. Wiseman and J. 0. Hiles, Comp. J. 10 (1968), 338-343,
Number 46
250
line 18 6125176 62
For these reasons the A* A contrary example appears in exercise 7; the point i6 that
neither method clearly dominates the other, hence the simple
line 11 1/16177 65
each with a random lifetime, A* each equally likely to be the next one deleted.
tjsm new paragraph after line 6 1/16177 64
Our assumption that each deletion applies to a random reserved block will be valid if
the lifetime of a block is an exponentially-distributed random variable. On the other hand,
if all blocks have roughly the same lifetime, this assumption is false; John E. Shore has
pointed out that type A blocks tend to be "older" than type C blocks when allocations and
deletions tend to have a somewhat first-in-first-out character, since a scqucnco of adjacent
reserved blocks tends to be in order from youngest to oldest and since the most recently
allocated block is almost never type A. This tends to produce a smaller number of
available blocks, giving even better performance than the fifty-percent rule would predict.
[Cf. C/3 CM 20 (1977), 812-820.J
line -9 11/15/78 65
areas A/* areas of the same size
line 7 1/16/77 66
. A/-* ; John E. Shore, C/1 CM 18 (1976), 433-440.
yet another addition after line 7 2/28/78 67
. V ; Norman R. Nielsen, CACM 20 (1977), 864-873.
exercise 28 4/19/77 68
line 2: 5; for A/* 5. For
line 4: ” A^* The execution time is 2u.”
line 8 6/25/76 69
V-l.] A^* V-l; and see especially also the work of Konrad Zuse, llcrichte der
Gesellschaft fur Math, und Datenv. 63 (Bonn, 1972), written in 1945. Zuse was the first
to develop nontrivial algorithms that worked with lists of dynamically varying lengths.]
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
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line -7
12119/76 70
is divisible is not divisible
6/25/76 7/
lines -15 thru -13: The A-l ... code; **v* The machine language for several early
computers used a three-address code to represent the computation of arithmetic
expressions;
lines -11 and -10: the A-l compiler language •'V* an extended three-address code
2L # %£(9 line 2 3/ 2/77 72
The latter Weizenbaum’s
several changes 12119/76 73
line 1: . • / \r+ ,
line 4: older other
new paragraph to be inserted after line 4:
A related model of computation was proposed by A. N. Kolmogorov as early as 1952.
His machine essentially operates on graphs C, having a specially designated starting vertex
Vq. The action at each step depends only on the subgraph G 'consisting of all vertices at
distance < n from vq in G, replacing G' in G by another graph G" w f(G'\ where G'
includes vq and the vertices v at distance exactly n from hq, and possibly other vertices;
the remainder of graph G is left unaltered, its components arc attached to the vertices v at
distance n as before. Here n is a fixed number specified in advance for any particular
algorithm, but it can be arbitrarily large. A symbol from a finite alphabet is attached to
each vertex, and restrictions are made so that no two vertices with the same symbol can be
adjacent to a common vertex. (See A. N. Kolmogorov, Uspckhi Mat. Nauk 8,4 (1953), 175-
176; Kolmogorov and UspenskiT, Uspckhi Mat. Nauk 13,4 (1958), 3-28, f\mar. Math. Soc.
Translations, scries 2, 29 (1963), 217-245.) Such graph machines can easily simulate the
linking automata defined above, taking one graph step per linking step; conversely, linking
automata can simulate graph machines, taking at most a bounded number of steps per
graph step when n and the alphabet size are fixed. The linking model is, of course, quite
close to the operations available to programmers on real machines, while the graph model is
not.
exercise 44 line 2 11/12/76 74
x k * yi -V* Xj+y k
line 8 1/16/77 75
(to appear) 'V* 13 (1975), 251-261.
QJUfSS line 1 7/31/76 76
Faa Faa
Page 34
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4119/77 77
UJQtiff new answer, continued
For example, F.q. (6) holds for all complex k and n, except in certain cases when n is a
negative integer; Eqs. (7), (9), (20) are never false, although they may occasionally take
indeterminate form6 such as 0 co or oo+oo. We can even extend the binomial theorem (13)
and Vandermondo’s convolution (21), obtaining 2 k ( *° + k * (l + *) r and
2 c , formulas which hold for all complex r, a, *, o, b whenever
the series converge, provided that complex powers are properly defined. [See L. Ramshaw,
Inf. Proc. Let tar i 6 (1977), 223-226.]
new answer 11112/76 78
42. l/(r+l)B(fc+l,r-k+l), if this is defined according to exercise 41(b). In general it appears
best to define (£) ■ 0 when k is a negative integer, otherwise (fc) m lim 4 _, r
r(s+l)/r(fc+l)r(s-k+l), since this preserves most of the important identities.
line 9
11/13/78 79
Polya A*
Polya
exercise 7
11/13/78 80
(It is "Glaisher’6 constant” 1.2824271...) To A* To
This formula ... n=4. A* (The constant /\ is "Glaisher’s constant” 1.2824271..., which R.
W. Cosper has proved equal to (2ire7 f_ f (2)/f(2))l/12 )
21,SEE exercise 5 11/29/77 81
line 1; 2n-l A* 2n+l
line 2: has ... dx. A* changes sign at r ■ n - O(Vn), so R m 0(f Q n \f"[x)dx) ■ 0(|/'(r)|) +
0(|/'(n)|) - 0(/(n)/Vn).
£„EE2 exercise 17(b) line 6 5/ 2/77 82
J2NN A^» J2P
H„EE2 exercise 19 4/19/77 83
24 A* 42
l+l)u A* 10+10)u
exercise 25 4/19/77 84
lines 11-12: operations” A* operations,” jumps on register even or odd, and binary shifts
last line: M. A* M, and others could set register«-rA, register«-rX.
Number 46 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park. CA 94025
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Page 35
km®
6/14177 S5
line 1: 6 A/-» 5 (also make this change in previous correction no. Ill)
line 6: 3434 A^* 3495 and 6 A* 5
line 7: 3495 A^» 3496 and 5 **V* 4
line 9: 3506 A^» 3505 and 6 A/* 5
line 10: 16 A* 14
changes to answer 14
6114177 86
line 1: uses as much due in part to J. Petolino uses a lot of
line 2: as possible, in in
line 9: INCX 1 A*
line 10: G A»* GMINUS1
lines -17 to end of page, replace by:
INCA 61
STA CPLUS60
MUL =3//4+l*=
STA XPLUS57(1:2)
CPLUS60 ENTA *
MUL =8//25+l=
GHINUS1 ENT2 *
ENT1 1,2
INC2 1,1
1NC2 0,2
1NC2 0,1
INC2 0,2
INC2 773,1
rA - Z + 24
E5.
rll ■ G
rI2 - 11C + 773
XPLUS57 INCA-*, 2
rA - 11C+Z-K+20+24 30 (> 0)
more changes to answer 14
6114/77 87
delete the bottom line and replace lines 1-31 by:
SRAX 5
D1V =30- rX m E
DECX 24
JXN 4F
DECX 1
JXP 2F
JXN 3F
DEC1 11
J1NP 2F
3H I NCX 1
2H DECX 29 E6.
4H STX 20111NUSN (0:2)
LDA Y E4.
MUL -1//4+1-
ADD Y
SUB XPLUS57(1:2) rA ■ D-47
20111 NUSN ENN1 *
INCA 67,1 E7.
SRAX 5 rX m D * N
DIV =7-
SLAX 5
DECA -4,1 rA-31-N
JAN IF E8.
DECA 31
CHAR
LDA MARCH
JMP 2F
1H CHAR
LDA APRIL
Page 36
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
253
new answer
6114177 88
15. The first such year is A.D. 10317, although the error almoit leads to failure in A.D.
10108+19* for 0 < * < 10.
2I„S2!>§ still more changes to answer 14 6114177 89
replace lines 1-6 by:
BEGIN ENTX 1950
ENTG 1950-2000
jnP EASTER
1NCG 1
ENTX 2000,5
JGNP EASTER+1
"driver”
routine,
uses the
above
subroutine.
£.££*2 line 18 11129/77 90
time. time. (It would be faster to calculate r f| (l/m) directly when m is small, and
then to apply the suggested procedure.)
£,£££ bottom line 11/29/77 91
Bcrk’ly A** Berkeley
£,£££i lines -4,-3 4/19/77 92
3)+7 •'V* 7.5)+16
£„££^ exercise 12 lines 7-10 5/27/78 93
delete "Thus, ...(b).”
£,£££ line 5 5/27/78 94
19-27. A^ 19-27; E. G. Cate and D. W. Twigg, ACM Tram. Math. Software 3 (1977),
104-110.
new answer 9/21/76 95
30. To insert, set P <= AVAIL, 1NF0(P) <- Y, LINK(P) «- A, if F ■ A then F <- P
else LINK (R) «- P, and R «- P. To delete, do (9) with F replacing T.
exercise 18 3/ 2/77 96
denotes, ... arc included. A*** denotes "exclusive or.” Other invertible operations, such as
addition or subtraction modulo the pointer field size, could also be used. It is convenient
to include
Number 46 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
254
Page 37
exercise 2
SI 2177 97
Page 38
line 2: next ... list point next, so the links in the list must point
line 3: So ... the Deletion at both ends therefore implies that the
line 4: ways. A/-* ways. On the other hand, exercise 2.2.4-18 shows that two links can be
represented in a single link field; in this way general deque operations are possible.
J0>»SSI3 exercise 9 step G4 S/ 2177 98
desired girls, A^» young ladies desired,
line -6 5/27178 99
"pedigrees”, A^» "pedigrees,”
exercise 12 line 5 9121/76 100
oo. • / \* oo. Here c{i,j) means c(/,i) if j < ».
answer 5 1/ 5/79 101
There is ... exist. “V* When n>l, the number of series-parallel networks with n edges is
2e n [see P. A. MacMahon, Proc. London Math. Soc. 22 (1891), 330-339].
fourth line before exercise 33 5/27/78 102
minimal. minimal. [This argument in the case of binary trees was apparently first
discovered by C. S. Peirce in an unpublished manuscript; see his New Elements of
Mathematics 4 (The Hague: Mouton, 1976), 303-304.]
QJi&Q updates to previous change number 150 9/21/76 10S
to appear, A^» 491-500,
(see also the important new contribution by H. G. Baker, Jr., C/1CM 21 (1978), 280-294, for
which 1 will probably want to revise Section 2.3.5 entirely!)
update to previous change number 151 11/29/77 104
Clark’s list-copying algorithm appeared in CACM 21 (1978), 351-357, and Robson’s in
CACM 20 (1977), 431-433
last line of answer 6 1/16/77 105
list. ' / \* list. For an alternative improvement to Algorithm A, see exercise 6.2.3-30.
exercise 8 6/25/76 106
line 1: also set R A* also set 11 «- oo, R
line 3: If R ■ A or M A* If pj
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 46
255
QJ21 exercise 26 line 3
2128178 107
two. A/* two, with blocks in decreasing order of sise.
P > fl A* P > M - 2*.
£1,(1(1121 program line number 12
i A* j.
new answer
31. See David L. Russell, SIAM J. Computing 6 (1977), 607-621.
H„(£illIS addition to previous change 153
.] A»* ; Lars-Erik Thorelli, BIT 16 (1976), 426-441.
21„l£lM exercise 41, numerator in value of a[5]
19559 A* 18535
delete A-l compiler, 458.
Aardenne-...
Taniana A/* Tatyana
AMAf A* AMM
turn
Baker, Henry Civens, Jr., 594.
add p487 to entry for Binomial theorem, generalizations of
Bobrow entry
add p420
4119/77 108
2128178 109
4119/77 110
6114/77 111
6/25/76 112
11/29/77 US
12/19/76 114
5/27/78 115
4/19/77 116
9/21/76 117
To be continued in future issues.
Number 46
256
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Random Ruminations
On Networks
Of The Future
BY JONATHAN SACHS
The Orthocode Corporation
6713 Richmond Avenue
Richmond View, CA 94805
We asked Jonathan Sachs to speculate
theoretically about networks and the
future ....
Popular Use of Networks: What It Will
Take
In the past, computers have been attractive
only to those oddballs who were interested
in computer hardware or software. Networking
can make them attractive to everyone who
needs to deal with information by making them
potential tools for processing information
about the world at large. This promises to be
the first development that makes computers
directly useful to a large proportion of man¬
kind.
There has been a great deal of speculation
(and some research) on this question of how
computers will affect the quality of life. Sce¬
narios run the gamut from a plugged-in society
where everyone is in touch with everything,
to a totally dehumanized society where people
interact with machines to the exclusion of one
another. For a thorough and responsible
(but highly readable) study of the issues, see
The Network Nation by Hiltz and Turoff
(Addision-Wesley Publishing Company).
Networks must be not only useful, but
usable by the public, or they will win little
acceptance. What do I mean by “the public?”
I mean: a substantial proportion of everyone
who lives in the part of the world we’re con¬
sidering. Here are some important character¬
istics of the public a successful network must
serve:
• It includes large numbers of people with
different technical orientations: toward com¬
puter programming, law, sculpture, animal
husbandry, etc.;
• It includes large numbers of peole who have
no technical orientation at all;
• Its members would demand widely varying
types and amounts of information from a net¬
work;
• Most of its members would have little or
no motivation to learn to use a network,
except for whatever immediate benefits they
could anticipate before they started.
To serve this audience, a network must be
usable (at least on an elementary level) by
non-technical people of average intelligence,
with very little training.
But a successful network must also be
able to accommodate experienced users with
sophisticated demands. Is this requirement for
power and versatility at odds with the equally
important need for ease of use? Not necessarily.
We could design a powerful system that
could be “packaged” in a variety of simple
ways for relatively specialized uses. One can
imagine network customers ordering options
from a network service representative, just as
telephone subscribers order different kinds of
service from the phone company. Users willing
and able to do so could build their own service
packages.
The early packaged offerings of such a ser¬
vice would probably be digital analogs of news¬
papers, telephones, and other things the public
is already comfortable with.
Less conventional uses would follow in time.
For example, one can imagine a “therapy group”
network conference in which every member
but the leader was guaranteed to remain anony¬
mous, or an “information brokerage” that acts
like a combination of publicity agency and
clipping service, putting generators and con¬
sumers of information in touch with each
other.
A single system accommodating both be¬
ginners and old hands would have a built-in
mechanism for introducing innovation to the
mainstream of use. It is the simple fact that
there would be no sharp dividing line between
an experimental use and a publicly available
one. When an advanced user developed an
application that was genuinely useful to the
public, the public would begin to use it. At
some point the operators of the network would
see fit to offer that application as an official
service. Thus the network-using public would
serve as both a laboratory for developing new
applications and a lobby for adopting successful
ones.
A Trap for Designers
There’s a saying that the generals who plan
military strategy are always guilty of refighting
the last war. Perhaps network designers are
guilty of a similar error: designing networks
for the future that can be built from com¬
ponents available today.
It is difficult to design a system with com¬
ponents that do not yet exist, but it is pointless
to design an eminently buildable system that
turns out to be unsuccessful because it is not
suited to the needs of its users. If our goal is
to design a network that will be acceptable to
the general public, we must determine (1)
what capabilities such a net will have to have,
and (2) what present-day technology, if any,
can provide them at an economic cost. If no
suitable technology is at hand we may change
or compromise our goals, but we wll get no¬
where by trying to fit the system’s require¬
ments to the technology that is available.
To take a simple example, consider terminal
display versus hard copy. Most of the net¬
work-like systems so far available to the public
(chiefly television-based systems like England’s
Prestel) use display only. The display was
already available in the prospective user’s TV
set, while a hard copy printer would have to
be added at extra cost. But is display output
sufficient? Probably not. Unlike a television
set, a computer network is used primarily to
process information. And information, once
processed, must often be preserved in acces¬
sible form.
Why can’t information be stored electro¬
nically and displayed at need? Because electro¬
nically-stored information is not accessible
in the same sense that hard copy is. There are
countless things one can do to hard copy but
can’t do to a display; for example, one can:
• Fold it, tear it, or staple it to things.
• Mark it with a felt-tip marker.
• Scribble notes on it.
• Work with it while sitting in an easy chair.
• Take it along to the park.
• Place it next to several like objects in order
to compare, collate, or cross-reference them.
• Place it on a part of a desk where one will
unconsciously reach for it when one needs
it.
• Cherish it as a memento.
This is not to say that video displays are
not useful; only that hard copy has some func¬
tions that displays cannot usurp, and that
therefore a general-purpose information system
that offers no hard copy will have a hard time
gaining acceptance.
For another example, take image quality.
Today’s standard of quality seems to be the
dot-matrix printer. Is that good enough for a
public network?
Consider what kinds of information the
network will convey. Initially, at least, the
greatest volume of use will be in fairly predict¬
able replacements for older media.
Newspaper material? Newspapers contain
many pictures-not only for their information
value, but because most readers want the paper
to be an easy read, and are unwilling to di¬
gest solid blocks of text. Some parts of the
paper (comics, movie ads) are inconceivable
without pictures. Television, the only other
comparable medium, is all pictures. (Radio is
an unfair comparison; it has sound, and the
computer nework does not have that yet,
either.)
How about instructional material and re¬
ference material? Both tend to use a lot of
graphics at all levels of difficulty (in some
strata the graphics are called “equations”).
For computerized conferences or telecom¬
muting (working from one’s home through a
computer) the requirements are a little more
complex. In some situations words would be
sufficient, as they are in telephone conversa¬
tions, and the need for graphics would not
come up. But when graphics were necessary,
Page 40
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
257
there would be the added difficulty of giving
each user a way to input pictures as well as
output them. There would probably have to
be several ways to input pictures: through
keyboard commands, fingerpainting on a screen,
digitizing existing line or continuous-tone
images, etc.
So it appears that a generally useful public
network would have to offer both line draw¬
ing and halftone graphics, at least approaching
the quality of newspaper pictures, and pre¬
ferably somewhat better. Could a dot matrix
printer produce a satisfactory result? Maybe,
but that criterion would disqualify most of
the printers made today! If it is recognized as
necessary, a different kind of hardware must
be designed.
A long list of other questions could be asked
along the same lines. What sort of input de-
vice(s) will users want? How fast will transmis¬
sion have to be? Will color output be necessary/
desirable? What about color input?
Some Wild and Crazy Possibilities
While we’re on the topic of capabilities,
what options could we add to a public network
to make it more useful, interesting, or what¬
ever else?
Another way to ask the question is: what
limitations on the forms networked informa¬
tion can take have we unconsciously accepted,
and what could we do if those limitations
were removed?
Suppose we didn’t content ourselves with
moderately good black-and-white dot images,
but went for high resolution color. The things
the network could convey would now expand
to include aesthetically meaningful repro¬
ductions of artwork. The network might even
become a medium for creating original art.
And there are other things the network could
then accommodate, such as medical literature
and maps.
Graphics may be viewed as a liberation from
the restrictions of text. But it may also be
viewed as a restriction itself. Computers can
analyze and generate sound. Why shouldn’t
a network do so?
A possibility: computerized catalogs of
sound recordings. A user finds a recording he
wants through an index; then the computer
plays it through the network. Such a system
could be used to catalog sounds that were too
short to deal with readily in a conventional
recording library, e.g., individual bird calls.
Another possibility: a data base of digitized
music. Audiophiles could search and mani¬
pulate this data base directly, just as library
researchers could search and manipulate a data
base of text.
Another possibility: co-ordinated telecon¬
ferences (or classrooms, or dramatic perform¬
ances) which make simultaneous use of audio,
video, and computerized text/graphics. For
example engineers could discuss a design using
audio to communicate by speech, while using
computer graphics to develp the design, and
video to examine samples or the data.
The most significant developments in net¬
working are impossible to predict. They will
be products of genius, and so will be incon¬
ceivable until they start to happen!
Number 46
258
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 41
Displaying Two Columns
with North Star t K .r DS ° N
O.K. HUDSON
334 Oney Drive
San Antonio, Texas 78209
OE 12
CD FB 19
C3 14 26
C3 03 1A
OE OF
CD 04 27
OD
C2 FB 19
C9
3A 1C 1A
FE 00
CA 13 1A
3E 00
32 1C 1A
C3 F9 19
CD OC 27
3E OF
32 1C 1A
C9
SYMBOL TABLE
BLANK 19FB
ORG 19EE
*************************************************
* *
♦ DOUBLE COLUMN FILE LISTING *
* *
* SEE DDJ #39,43 *41,44 #42,44 *
* *
*************************************************
♦THIS PROGRAM REQUIRES PATCHES TO THE DOS AND AN
♦EXTRA SUBROUTINE IN RAM TO CAUSE THE DIRECTORY
♦LISTING TO BE PRINTED IN TWO COLUMNS.
♦THE EXTRA SUBROUTINE IS LOCATED AT 19EE BECAUSE
♦MY DOS PERSONALIZATION AREA IS FULL.
♦
♦IN ORDER TO GET CORRECT ADDRESSES ON FILES WHERE
♦THEY ARE NOT NORMALLY SPECIFED, ONE MUST DO A
♦ ’TY 'WHATEVER' 1 ADDRESS - THEN REPEAT WITH
♦THE PROPER FILE TYPE — THE ADDRESS WILL
♦BE REMEMBERED BY THE DISK FILE.
♦
♦THIS SOURCE WILL ALSO HANDLE THE OLD DOS IF THE
♦FOLLOWING EQUATES ARE SUBSTITUTED:
* DOS EQU 25EEH
* D0S2 EQU 2709H
* LFCR EQU 270FH
*
♦SYSTEM EQUATES FOR N^ DOS V.4
ORG EQU 19EEH
DOS EQU 2614H
D0S2 EQU 2704H
LFCR EQU 270CH
♦
♦IN ADDITION THE FOLLOWING PATCHES MUST BE MADE
♦ WITHIN THE DOS ITSELF I
♦ 2601 FE OA
2603 D2 EE 19
2611 CD F6 19
♦FOR THE OLD DOS (0.3 ?>,
♦ 25DB FE OA
♦ 25DD CA EE 19
♦ 25EB CD F6 19
♦
MVI C,12H
CALL BLANK
JMP DOS
JMP PSUB
REN MVI C,OFH
BLANK CALL D0S2
♦
♦
DCR C
JNZ BLANK
RET
♦
THE DOS PATCHES ARE:
I have enjoyed the contributions from
your other readers, and feel that now the
time is ripe for me to reciprocate. At¬
tached please find an 8080 Assembly
listing for making a North Star Disk
display its catalogue in two columns.
Several other contributors have addressed
this prolbem with varying degrees of
success. This program is different in
that it tries to make clear the required
changes for the ‘latest’ DOS (which I
think is V.4) and the old DOS (which
may be V.3). Both kinds are around—
in addition to some others too.
This program differs in one other im¬
portant aspect: the other programs re¬
lied on the terminal generating a carriage
return. This does not happen when a
printer is used. This program will generate
a carriage return after 80 spaces.
Keep up the good work. If you don’t
want to publish this, you may trash it.
I don’t believe in copyrights—and who
cares anyway. We mostly do this for fun
and if we also make a buck now and then
— fine.
♦THIS IS THE SPACE ALLOWED FOR AN ENTRY
♦THIS SUBROUTINE IS ALREADY IN THE DOS
♦GET ANOTHER ENTRY
♦DOS RE-ENTRY POINT
♦THIS IS THE SPACE BETWEEN COLUMNS
♦ THIS IS THE ACTUAL SOURCE OF I HE BLANKS
WITHIN THE DOS - IF YOU WANT SOME
OTHER CHARACTER YOU MAY PATCH IT IN !
♦COUNT THE BLANKS REMAINING TO BE SENT
♦FINISHED ??
♦SUBROUTINE TO PROVIDE LINE FEED AND CARRIAGE RETURN
♦
PSUB LDA ST0R1
CPI 0
JZ DSUB
MV I A, 0
STA STOR1
JMP REN
DSUB CALL LFCR
MVI A,OFH
STA ST0R1
RET
♦
♦
♦STORAGE TABLE
ST0R1 DW 0
♦SAVE THE ACCUMULATOR VALUE
♦WAS IT A 0 ??
♦IF IT WAS THEN LINE FEED AND CARR RET
♦MAKE SURE IT IS A 0 NEXT TIME
♦BY PUTTING IT IN STORAGE
♦GO PRINT THE NEXT ENTRY
♦THESE ARE ALSO IN THE DOS - USE 'EM
♦MAKE SURE WE DON'T DO THIS TWICE IN A ROW
♦BY FILLING STORAGE WITH A PROPER FLAG
♦THIS IS WHERE WE KEEP THE FLAGS
DOS 2614
PSUB 1A03
D0S2 2704
REN 19F9
DSUB 1A13
ST0R1 1A1C
Page 42
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 46
259
A Versatile Memory Dump
BY HAL KNIPPENBERG
2514 Blueberry Drive
Augusta, GA 30906
Dear DDJ:
I am often asked how to develop memory
dump programs. The main complaint is that
most memory dump programs are too special¬
ized-they work only in one mode. For in¬
stance, they will dump Hex when you want
Decimal. Or they will dump Octal when you
want Hex.
The program I have developed in answer to
these questions is a generalized MEMORY
DUMP program written in BASIC. It uses two
base conversion subroutines and can work in
four different modes. In addition, it prints
an ASCII dump as well.
I wrote the program in Digital Group’s
MAXI-BASIC. If being used with another
Iff
BASIC which uses LEFT, RIGHT, and MID
string functions, change the following:
LINE 500 AND 655 . .Change the A$(l,l) to LEFT $(A$,1)
LINE 725 .Change A$(I,1) to MIDS(A$,I,1)
LINE 915.Change H$(l,3) to LEFT$(H$,3) and
change H$(4) to RIGHT $(H$,3)
LINE 565 .Many BASICS use the command
PEEK instead of EXAM
I have used many REMARK statements to
help show the structure of the program, but
you do not need to type in any of the REM
lines for the program to work properly.
Two other lines might cause trouble, lines
240 and 510. MAXI-BASIC does not have a
quick way to clear the monitor, so I use a
machine language subroutine. TRS-80 users
can use CLS to do the same thing. If your
BASIC does not have a cleax-screen function,
GOSUB to the following BASIC subroutine:
FOR I = 1 to 16
PRINT
NEXT I
RETURN
This will also clear the screen, although it
takes a moment longer.
DiA©Ln®in®incDUia
-P-©COCOcn®® — — O
oinminuiLntncouxjoa
DistCDin®in®inc
!> ® — — CM CM CO CO ■«
-r-f-f-t-r-r-f-c
Disi<sist®Lr<®Ln®i/)a
iM/uoior-f-oscommc
- r- p- r- c- r- c- r- r- r- o
n®in®Ln®Ln®ui<2
0 CO 00 CO CO CO CO CO TO Ci
LSt®isiCDUi®inS>b
COCOCO®® — — CMC
cooo®m<r»cn<7><7>c
t ® in® in ® u
LO CO 0
J CM CM CM CM CM 0
-c-cococnco®® — —
MCMCMCMCMCMCOCOCOCO
®Ln®LTl®U 1 ®lJ
(MCMCOCO*--*-U1Lj
CO CO CO CO CO CO < 0 C
Dvn®in®tSi®Ln®isi®i/i®Lni3
- C- CO CO CO CO ® ® — — CM CM CO CO 1
')COCOCOCOCO*-TM-*-*-M-M-'*-'1
ocomco ® © - -
Number 46
260
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 43
BY EDWARD L. ELIZONDO
6 Cypress Court
E. Windsor, N.J. 08520
I was delighted to find in your Janu¬
ary issue not one, but two contributed
programs to convert Processor Tech¬
nology assembler format files to a format
compatible with the CP/M assembler.
I am presently running a 48K CP/M
system, using CUTER in ROM at C000
hex to drive a Processor Technology
VDM. My weekend project started with
the idea of converting the CUTER source
file (generously distributed by Processor
Tech on the CUTER/BASIC5 cassette)
to CP/M format, make a few alterations,
and reassemble it at F000 hex.
Unfortunately, neither published pro¬
gram quite met my requirements. Hollis
Frampton’s CPCON is limited to pro¬
grams smah enough to fit in memory
and requires downloading to tape, while
Mark Zeiger’s CHANGE did not correctly
copy with commented lines, ASC pseudo¬
ops and other ALS-8 peculiarities such
as dummy period operands.
Since frustration is the spur of creat¬
ivity, I took it upon myself to generate
yet a third conversion program, herein
submitted to you.
ALS8CPM successfuhy converts the
bulk of ah ALS-8 statements to a form
digestible by the CP/M ASM. Using
ALS8CPM, the CUTER source files
(total size = 58K) were converted with
only seven residual errors flagged by
ASM on reassembly. The program is
fairly straightforward and fully com¬
mented, so it can easily be modified if
desired.
A few comments about the program:
I chose not to convert negative numbers
used in immediate operands (MVI A,
— 1) for fear of creating subtle errors in
programs using negative signs in arith¬
metic expressions. Not processed by
ALS8CPM are the infrequent ALS-8
pseudo-ops COM, NST and LST, the
INTEL pseudo-op TITL, and program
use of ASM reserved words such as
SET, IF and ENDIF. Also not handled
are PSW and SP equate statements used
to add these register names to the ALS-8
symbol table ( an unforgiveable commis¬
sion on the part of the late Processor
Tech). Residual errors after conversion
involving any of the preceding can
quickly be located by a trial reassembly
and corrected by editing.
I intend to submit this program to
the CP/M User’s Group and to the Pro¬
cessor Technology User’s Society (PRO¬
TEUS). Incidentally, even though I have
never owned a SOL, I must publicly
compliment Stan Sokolov and the latter
group for three years of publishing an
excellent newsletter and attempting to
protect the member’s investment in time
and money by providing a wealth of
information, reviews, valuable user feed¬
back on various commercial products,
tutorials on such diverse subjects as
PASCAL and CP/M, and much inside
information on what really was hap¬
pening at Processor Tech.
For any impatient souls out there who
don’t feel like typing up ALS8CPM,
I will provide the source code on an 8
inch standard CP/M format diskette for
$10 to cover the cost of the diskette,
mailer and shipping charges, until the user
group distributions are available.
ALS8CPM .ASH
PROGRAM FOR CONVERTING PROCESSOR TECHNOLOGY
ALS-8/SPKG-1 ASSEMBLER FILES TO CP/M FORMAT
(C) COPYRIGHT 1980
ED ELIZONDO 6 CYPRESS CT EAST WINDSOR NJ 08520
ALL RIGHTS RESERVED
THIS PROGRAM MAY BE USED FREELY BY COMPUTER
HOBBYISTS FOR NON-COMMERCIAL APPLICATIONS.
IT MAY NOT BE USED FOR COMMERCIAL APPLICATIONS
OR SOLD WITHOUT WRITTEN PERMISSION OF THE
AUTHOR.
REV 1.6 31 JAN 1980
NOTE: This program processes assembly language files
prepared for the Processor Technology ALS-8 or Software
Package No 1 assemblers to a format compatible with
the CP/M ASM assembler. It requires the presence of
CUTER/SOLOS or some other means of loading the ALS-8
source file onto memory so that it can be saved by CP/M.
It does not require the presence of anything other than
CP/M during the remaining operations.
The translation process operates in accordance with
the following algorithms:
Each line is converted independently. The line byte count
and line number fields are deleted from the source lines
and each line is terminated with a CR/LF sequence.
A semicolon is placed ahead of all comment lines (for
compatibility with MAC) and ahead of all comment fields.
Leading spaces are deleted from comment fields only.
Comment lines and the remainder of comment fields are
passed unchanged, except for deletion of any exclamation
mar ks.
Periods used as dimmy operands for formatting purposes
are removed, as well as any leading spaces appearing in
instructions and operand fields. Operands enclosed in
single quotes are passed unchanged.
a
ASC pseudo-operators are changed to DB and the corresponding
delimiters changed to single quotes.
The *>' pseud o- operator is converted to an 'AND 0FFH' post
operator and the '<’ is similarly converted to a 'SHR 8'.
Instruction, operand and comment fields are tabbed
and colons are added to labels to "pretty" the output.
The program utilizes slightly modified versions of the
CP/M User's Croup LI0S.ASM disk 1/0 routines (CPMUG 1.19)
TO USE: 1) load your ALS-8 format program into RAM at 100H
(If using SOLOS/CUTER, note the first two digits
of program size returned by the load message.
Convert to decimal and add 1 to obtain the
number nn required in step 3).
2) boot up CP/M
3) type SAVE nn NAME). EXT (where nn is number of
pages of program size in decimal)
H) run the conversion program by typing:
ALS8CPM NAME 1. EXT NAME2. ASM
where NAME2.ASM is the desired name of the CP/M
compatible output file (note spaces between
the above name fields)
5) edit the resulting ASM file to add the appropriate
0RG statem ent.
6) assemble to locate any residual unique errors.
BDOS
ADDRESSES:
BDOS:
E0U
0005
;BDOS ENTRY POINT
SOURCE:
E0U
5CH
;S0URCE FILE FCB
TBUF :
E0U
0080H
;TRANSFER BUFFER
BDOS
FUNCTION CODES:
PRINT:
E0U
9
OPEN:
E0U
15
CLOSE:
E0U
16
MAKE :
E0U
22
READ:
E0U
20
WRITE:
E0U
21
DELETE:
LQU
19
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park CA 94025
Number 46
ASCII
CODES:
SPACE:
EQU
20H
QUOTE:
EQU
27H
TAB:
EQU
09H
CR:
EQU
ODH
LF :
EQU
OAH
. •
MAIN
PROGRAM »
;
ORG
100H
LXI
DAD
H, 0
SP
;GET OLD STACK POINTER
SHLD
OLDSTK
;SAVE IT FOR EXIT
LXI
SP,NEW STK
;SET UP NEW STACK
LXI
D.MSSGO
;SAY HELLO
CALL
MESSAGE
CALL
GETNAMES
;GET FILE NAMES FROM COMMAND
CALL
OPE NFILES
;0PEN F ILES FOR ACCESS
LXI
D,MSSG8
;WE’RE DOING FINE
CALL
MESSAGE
CALL
PROCESS
;PROCESS LINE BY LINE
CALL
W EOF
;F ILL LAST INCOMPLETE PAGE
ABEND:
CALL
CLOSEFILE
;CLOSE FILES
LXI
D,MSSG9
;WE’RE FINISHED
CALL
MESSAGE
FIN:
LHLD
SPHL
OLDSTK
;RESTORE OLD STACK POINTER
RET
•.RETURN TO CP/M
o
GETNAMES
SUBROUTINE TO CHECK & GET FILE NAMES
GETNAMES:
LDA
CPI
JZ
LDA
CPI
JZ
SOURCE+1
SPACE
ERROR6
SOUR CE+1 7
SPACE
ERROR7
FIRST CHAR OF SOURCE NAME
EMPTY?
YES, ERROR
FIRST CHAR OF DEST NAME
EMPTY?
YES, ERROR
MOVE DEST FCB TO SAFE PLACE
LXI
LXI
M VI
CALL
D, SOURCE + 16
H,DEST
B , 16
MOVE
INITIALIZE FCB 'S
XR A A
STA SOURCE+32
STA DEST+32
RET
START OF TEMP DEST FCB
WORKING DEST FCB
NUMBER OF FCB CHARACTERS
MOVE NAME
GET A 0
ZERO SOURCE NR FIELD
ZERO DEST NR FIELD
0 P
E N F ILES
•
SUBROUTINE
TO OPEN FILES FOR
ACCESS •
)PENF ILES:
M VI
C,OPEN
;GET OPEN FUNCTIOI
LXI
D,SOURCE
CALL
B DOS
;OPEN SOURCE FILE
CPI
OFFH
;OPEN ERROR?
JZ
ERROR 1
;YES, ABORT
M VI
C,DELETE
;DELETE FUNCTION
LXI
D,DEST
CALL
B DOS
;DELETE EXISTING I
M VI
C.MAKE
;MAKE FUNCTION
LXI
D,DEST
CALL
B DOS
•.CREATE NEW DEST 1
CPI
OFFH
;MAKE ERROR?
JZ
ERROR 3
; YE S, ABORT
M VI
C .OPEN
;OPEN FUNCTION
LXI
D, DEST
CALL
B DOS
;OPEN DEST FILE
RET
P R
0 C E S S
*
ROUTINE TO
PROCESS EACH LINE
•
PROCESS:
XR A
A
;CLEAR STRING FUG
STA
FLAG
CALL
GETBYT
;GET LINE CHAR COUNT
CPI
1
;END OF FILE?
JZ
EOFMARK
;YES, PROCESS IT
DC R
A
•.UPDATE CHAR LINE COUNT
STA
EOLC NT
;SAVE IT
M VI
B ,5
;F IELD COUNT
o
LNUM:
PUSH
B
MOVE PAST LINE NUMBER FIELD
CALL
GETBYT
READ A BYTE
POP
B
CALL
COUNT
DECREMENT LINE COUNT
JZ
PR EMEND
PREMATURE END OF LINE
DC R
B
DECREMENT FIELD COUNT
JNZ
LNUM
UNTIL DONE
LABEL:
CALL
GETBYT
PROCESS LABEL FIELD
CPI
• • i
COMMENT LINE?
JZ
COMLINE
YES, PROCESS IT
CPI
SPACE
MISSING LABEL?
JZ
INSTR
THEN PROCESS INST
LA BEL 1:
CALL
OUTBYT
OUTPUT LABEL CHAR
CALL
COUNT
DECREMENT LINE COUNT
JZ
EOLINE
IF END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
SPACE
END OF ALS-8 LABEL?
JZ
LABEL2
YES, EXIT LOOP
C PI
': '
END OF INTEL LABEL?
JNZ
LA BEL 1
NO, KEEP GOING
UBEL2:
M VI
A ,' : •
YES, OUTPUT A COLON
CALL
OUTBYT
AND DROP THRU
INSTR:
M VI
A , TAB
PROCESS INSTR FIELD
CALL
OUTBYT
TAB TO NEXT COLUMN
CALL
DELSP
DELETE LEADING SPACES
JC
EOLINE
IF END OF LINE
■
CHECK FOR ASC PSEUDO-OP
CPI
'A '
POSSIBLE ASC PSEUDO OP?
JNZ
INSTR2
NO WAY
CALL
COUNT
DECREMENT LINE COUNT
JZ
EOLINE
IF END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
'S '
ASC PSEUDO OP?
JNZ
REC0V2
NO, RECOVER LAST TWO BYTES
CALL
COUNT
DECREMENT LINE COUNT
JZ
EOLINE
IF END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
•c •
ASC PSEUDO OP?
JNZ
REC0V3
NO, RECOVER LAST 3 BYTES
*
CONVERT
ASC PSEUDO OP TO
DB
LXI
D, DBOP
OUTPUT A 'DB'
CALL
PUTSTRING
M VI
A , TAB
END OF INSTR FIELD
CALL
OUTBYT
TAB TO NEXT COLUMN
*
HANDLE
ASC OPERAND AND CONVERT DELIMITERS
CALL
DELSP
DELETE EXTRA SPACES
JC
EOLINE
IF END OF LINE
STA
DELIM
SAVE THE ASC DELIMITER
M VI
A,QUOTE
GET CPM DELIMITER
ASC 2:
CALL
OUTBYT
OUTPUT IT
CALL
COUNT
DECREMENT LINE COUNT
JZ
EOLINE
IF END OF LINE
LDA
DELIM
GET DELIMITER
MOV
B , A
INTO B
PUSH
B
SAVE B
CALL
GETBYT
GET NEXT BYTE
POP
B
RESTORE B
CMP
B
DELIMITER?
JNZ
ASC 2
NO, KEEP GOING
M VI
A,QUOTE
YES, GET CPM DELIMITER
CALL
OUTBYT
OUTPUT IT
JMP
COMMENT
REMAINDER MUST BE COMMENT
RECOVER
LAST TWO BYTES (NOT ASC PSEUDO OP)
REC0V2:
STA
TEMP2
SAVE LAST BYTE
M VI
A , ' A '
F IRST BYTE WAS AN ’A *
CALL
OUTBYT
OUTPUT IT
LDA
TEM P2
GET LAST BYTE
JMP
INSTR2
CONTINUE NORMALLY
RECOVER
LAST 3 BYTES (NOT ASC PSEUDO OP)
REC0V3:
STA
TEMP2
SAVE LAST BYTE
LXI
D,ASOP
WE KNOW LAST 2 BYTES WERE 'AS
CALL
PUTSTRING
SO OUTPUT THEM
LDA
TEM P2
GET LAST BYTE
;
HANDLE
REMAINDER OF INSTRUCTION FIELD
INSTR2:
CALL
PASS
OUTPUT REST OF FIELD
JC
EOLINE
;IF END OF LINE
OPERAND
M VI
A, TAB
PROCESS OPERAND FIELD
CALL
OUTBYT
TAB TO NEXT COLUMN
CALL
DELSP
DELETE LEADING SPACES
JC
EOLINE
IF END OF LINE
|
CHECK FOR ’<• SPECIAL OPERATOR
OPE R 1:
CPI
'<•
LEFT BYTE MASK?
JNZ
0PER3
NO WAY
CALL
COUNT
DECREMENT END OF LINE COUNT
JZ
EOLINE
IF END OF LINE
CALL
GETBYT
GET NEXT BYTE
CALL
PASS
OUTPUT REST OF FIELD
JC
EOLINE
IF PREMATURE END OF LINE
LXI
D, LB YT E
OUTPUT A SHIFT RIGHT EXPR
CALL
PUTSTRING
JMP
COMMENT
REMAINDER MUST BE COMMENT
CHECK FOR •>• SPECIAL OPERATOR
0PER2:
CPI
RIGHT BYTE MASK?
JNZ
OPE R 3
NO WAY
Number 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 45
262
CALL
COUNT
{DECREMENT LINE COUNT
JZ
EOLINE
;IF END OF LINE
CALL
GETBYT
;GET NEXT BYTE
CALL
PASS
{OUTPUT REST OF FIELD
JC
EOLINE
;IF END OF LINE
LXI
D, RBYTE
;THEN A MASK RIGHT EXP
CALL
PUTSTRING
JMP
COMMENT
{REMAINDER MUST BE COMMENT
J
HANDLE
REMAINDER OF OPERAND
OPE R 3:
CPI
QUOTE
IS IT A QUOTE?
CZ
TOGGLE
YES, TOGGLE STRING FLAG
CPI
• .»
IS IT A PERIOD?
JZ
STRING
YES, CHECK IF PART OF STRING
CPI
SPACE
IS IT A SPACE?
JNZ
OPERK
NO, PROCESS IT
STRING:
STA
TEMP
SAVE BYTE
LDA
FUG
IS CHAR WITHIN STRING?
ORA
A
JZ
COMMENT
;N0, END OF OPERAND FIELD
LDA
TEMP
;YES, GET BACK BYTE
0PER4:
CALL
OUTBYT
{OUTPUT BYTE
CALL
COUNT
{DECREMENT LINE COUNT
JZ
EOLINE
;IF END OF LINE
CALL
GETBYT
{GET NEXT BYTE
;
JMP
0PER3
{KEEP GOING
COMLINE
PROCESS COMMENT LINE
M VI
A , • ; *
GET A SEMICOLON
JMP
CLOOP
OUTPUT IT 4 REST OF LINE
COMMENT
PROCESS COMMENT FIELD
M VI
A , TAB
CALL
OUTBYT
TAB TO NEXT COLUMN
M VI
A ,' ; •
GET A SEMICOLON
CALL
OUTBYT
OUTPUT IT
CALL
DELSP
DELETE LEADING SPACES
JC
EOLINE
IF END OF LINE
CPI
• ! *
EXCLAMATION MARK?
JZ
CL00P2
YES, DELETE IT
CLOOP:
CALL
OUTBYT
NO, OUTPUT IT
CL00P2:
CALL
COUNT
DECREMENT LINE COUNT
JZ
EOLINE
IF END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
• !’
EXCLAMATION MARK?
JZ
CL00P2
YES, DELETE IT
JMP
CLOOP
KEEP GOING
PREMEND
PREMATURE END OF LINE
M VI
A , CR
OUTPUT A CARRIAGE RET
CALL
OUTBYT
EOLINE:
MVI
A, LF
NORMAL END OF LINE
CALL
OUTBYT
OUTPUT A LINE FEED
JMP
PROCESS
PROCESS NEXT LINE
EOFMARK
MVI
A, • Z ’-40H
GET A C PM EOF MARK
CALL
OUTBYT
OUTPUT IT
RET
EXIT PROCESS
TOGGLE:
PUSH
PSW
FUG SET IF STRING IN QUOTES
LDA
FUG
TOGGLE FLAG
CMA
STA
FUG
THAT’S ALL
POP
PSW
RET
*
DELETE
EXTRA SPACES
DELSP:
CALL
COUNT
DECREMENT LINE COUNT
JZ
DELSP2
IF PREMATURE END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
SPACE
SPACE?
JZ
DELSP
YES, DELETE IT
ORA
A
RESET CARRY FUG
RET
RETURN WITH BYTE
DELSP2:
STC
SET CARRY FUG FOR EOL
RET
RETURN WITH FLAG SET
OUTPUT
BYTES UNTIL END OF
FIELD
PASS:
CALL
OUTBYT
OUTPUT BYTE
CALL
COUNT
DECREMENT LINE COUNT
JZ
PASS 2
IF PREMATURE END OF LINE
CALL
GETBYT
GET NEXT BYTE
CPI
SPACE
END OF FIELD?
JNZ
PASS
NO, KEEP GOING
ORA
A
RESET CARRY FUG
RET
RETURN WITH SPACE
PASS 2:
STC
SET CARRY FLAG FOR EOL
RET
RETURN WITH FLAG SET
COUNT:
LDA
EOLC NT
DECREMENT END OF LINE COUNT
DC R
A
STA
EOLC NT
THAT’S ALL
RET
PUTSTRING •
ROUTINE TO OUTPUT A STRING TO DISC »
PUTSTRING:
LDAX D ;GET A BYTE
CPI ’$ ’ ;TERMINATOR?
P
RZ
PUSH
D
CALL
OUTBYT
POP
D
INX
D
JMP
PUTSTRING
CANNED STRINGS: •
ASOP:
DB
•ASS’
DBOP:
DB
'DBS'
RBYTE:
DB
' AND
OFFHS
LBYTE:
DB
’ SHR
8$’
YES, RETURN
SAVE D&E
NO, OUTPUT BYTE
RESTORE DAE
BUMP POINTER
KEEP GOING
STRING TO RECOVER AS STRING
STRING TO REPLACE ASC OP
STRING TO REPLACE ">" OP
STRING TO REPLACE ’’<" OP
0 U T B Y T
ROUTINE TO OUTPUT A BYTE
INPUT: A =B YT E
OUTBYT: STA
TEMP
SAVE BYTE
OUT 1: LXI
H , OB UF ♦I 28
XCHG
.BUFFER END A DDR IN DE
LHLD
OUT PT
{CURRENT A DDR IN HL
CALL
C PHL
{TEST FOR END OF BUFFER
JZ
OUT 2
YES, WRITE
LDA
TEMP
MOV
M , A
STORE DATA BYTE IN BUFFER
INX
H
BUMP BUFFER POINTER
SHLD
OUT PT
SAVE BUFFER POINTER
ORA
A
RET
EXIT
OUT 2: LXI
D, OB UF
POINT TO OUTPUT BUFFER
LXI
H , TB UF
TEMP BUFFER
MVI
B , 128
CALL
MOVE
COPY BUFFERS
MVI
C,WRITE
WRITE FUNCTION
LXI
D,DEST
OUTPUT FCB
CALL
B DOS
ISSUE WRITE
CPI
OF F H
JZ
ERROR 3
CPI
2
JZ
ERR0R4
C PI
1
JZ
ERR0R5
LXI
H, OB UF
RESET POINTER
SHLD
OUT PT
JMP
OUT 1
CONTINUE
{ G E
T B Y T
»
•
; ROUTINE TO
READ A BYTE
*
; OUTPUT:
A =B YT E
•
GETBYT: LXI
H, IB UF ♦! 28
XCHG
BUFFER END A DDR. IN DE
LHLD
INPTR
CURRENT POINTER IN HL
CALL
C PHL
TEST FOR END OF BUFFER
JZ
GETB2
YES, READ
GETB1: MOV
A , M
GET BYTE
INX
H
BUMP POINTER
SHLD
INPTR
SAVE POINTER
ORA
A
RESET CARRY
RET
GETB2: MVI
C,READ
READ FUNCTION
LXI
D,SOURCE
FCB ADDRESS
CALL
B DOS
ISSUE READ
CPI
0
ERROR?
JNZ
ERR0R2
YES
LXI
D, TBUF
POINT TO TEMP BUFFER
LXI
H , IB UF
INPUT BUFFER
MVI
B , 128
CALL
MOVE
COPY BUFFER
LXI
H, IB UF
RESET BUFFER POINTER
SHLD
INPTR
JMP
GETB 1
CONTINUE
; m
0 V E
«« ft
•
; ROUTINE TO
MOVE BLOCKS OF DATA •
MOVE: LDAX
D
GET BYTE
MOV
M , A
STORE BYTE
INX
H
INX
D
BUMP POINTERS
DC R
B
DECREMENT COUNT
JNZ
MOVE
LOOP
RET
ROUTINE TO COMPARE HL VS DE
MOV
A , H
CMP
D
RNZ
MOV
A ,L
CMP
E
Continued on page 48
Page 46
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
263
algebra anak
Another approach to the interchange
problem uses a swap primitive. It works
by simply exchanging the smaller segment
to put it into its proper position and
then applying the same procedure to the
remaining segment which itself requires
an interchange. A C program which does
this is given below:
BY DENNIS ALLISON
MERGE SORT REVISITED
My old friend, Sylvan Rubin, sent
on to me a major improvement in the
nonrecursive merge program published in
DDJ # 44. Rather than build the merged
list backwards and then, later, reverse it,
he builds it in the right order to begin
with. This cuts the number of assign¬
ments per data element from 9.5 to 4.5
assuming randomly distributed data. He
also improved the control structure a
bit to eliminate some tests. All in all
a much better program.
fashion. In the real world, here is a trade¬
off. Recursive code is usually smaller
and shares temporary random access
memory with other disjoint computa¬
tions; interactive code is usually longer,
uses dedicated storage, and runs much
faster. Which form of algorithm one
wants to use depends upon the applica¬
tion.
INTERCHANGE AGAIN
Richard Karp pointed out two other
solutions to the interchange problem
int aC803;
interchange (n,n) int «,n; <
int i,j f k;
i * i;
n * n-n; /• n and « are segment sizes */
for<;;) <
k * <«>n)?n:«;
if(k»*=0) return;
swap(i, i+n+n-k, k);
if(«<n) <
n *-
> else <
i «♦ n;
n =- n;
swap < i, j, k ) int i,j f k; <
register int t;
while(k—) <
t * aCi3; ati+O = aC j 3;
aCj♦♦3 * t;
>
>
/# MERGE algorithm using linked lists.
/t written in C. 24 Mar 80 Sylvan Rubin» Algorithmic Eng.
merge <i»J) int irj> -C int t*k»i*$
if<aCi3<a[JD) < m=i» i=J» J=m»>
t=i» k.=t»
i = 1ink C i 3 J
while(i1=0) <
if<aCi3<aCJ3)
1 ink.Ck.3=i f /#
k=i »
i*linkCi3»
<m=i» ia'J* J=m»>
link next largest element to tail of
merged list
1 inkCk.3=J» /*
return (t)»
link remaining list to tail of merged list
RECURSION VERSUS ITERATION
Sylvan comments that he doesn’t
think that we should publish the recur¬
sive form of algorithms since their trans¬
lation into assembler or BASIC is a non¬
trivial task. I don’t completely agree.
The purpose of this column is to ex¬
pose some of the fundamental mecha¬
nisms behind algorithmic solutions and to
gain some appreciation of the aesthetics.
That goal must involve recursion in some
presented last time. And I decided I
should have said something about the
shift-register version.
The shift-register version requires m* n
operations. The idea is to start at the
shortest segment, pluck out the element
at the end, move everything over one
(to the right or the left depending upon
which end the shortest segment appears)
stick in the selected element and repeat
until the interchange is completed.
Graphically the procedure is
But the truly elegant solution is this
one attributed by E.W. Dijkstra to J.
Ichbiah. One needs an array reversal
primitive-an easy thing to do with a
single temporary. The algorithm is best
seen graphically:
One first reverses each of the segments
independently and then reverses the
entire array. Not as efficient as the group
theoretic scheme, but it does have a
pleasing aesthetic quality.
Number 46
264
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 47
BIT REVERSAL
There’s never really much call for an
algorithm to reverse the bits in a word.
Nonetheless, this algorithm, due to C.
Strachey [CACM 4:3 961 p. 146] is
interesting because of its aesthetic beauty.
To see how it works it’s best to
pretend we have a double length register
and write out the bits in the order we
have them and the order we want them.
We then write down the shifts required
to get each bit from where it is to where
it should be and write down the binary
representation for that number. We
then program a select-bits, shift, and
merge sequence for each power of two,
thus generating the result. Figure 1 shows
the whole procedure worked out for a
16-bit operand.
A double length register is not neces¬
sary. One can do it in place by observing
that after the selection one can shift
both operands, one right and the other
left. Further, one can use the same mask
to handle the selection. The C program
below will reverse the bits of a 16-
bit word. Note that only one more step
would be needed for a 32-bit word since
the complexity grows as the logarithm
of the number of bits.
There are, of course, several alternative
ways to accomplish the same task. The
Continued from page 46 -
• RET
p' o' n' m' 1' k' y i‘ h' g' f' e' d' c' b‘ a' a b c d e f g h 1 j k 1 m n o p
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 shift numbers
0000000011111111 shift 16
0000111100001111 shift 8
0011001100110011 shift 4
0101010101010101 shift 2
1111111111111111 shift 1
a be d e fg hi_j_k_l_mn > o_£ initial position
1jklm£££abcd£££h^. shift 16
mno£ijk^lef 2 £ab£d. shift 8
0£m£kl1j_gh_ef.cdab. Shift 4
.shift 2
poTimlkjihgfedcba. shift 1
Figure 1. Schematic Bit Reversal
int naskU <
OxFFFF, 0x5555, 0x3333, OxOFOF, OxOOFF
rtvtrit! val ) <
regnter int
i * val;
j * 8; k ■ 4;
while!j) {
i ■ (<ilMafkCk])«j)l((i»j)JnatkCk]);
j ■» l;
k—;
>
return!i);
obvious one of performing the reversal
a bit at a time is costly to perform in
place and is Unear in the length of the
word. A 16-bit word requires 16 opera¬
tions to reverse the bits. Anyone knowing
a good appUcation for bit-reversed data
won’t suggest the FFT (which leaves
its results in reverse binary order) since
there are better ways to reorganize its
result than direct selection.
On a byte-oriented processor it might
be better to have a table of reversed
bytes and simply look up each byte
of the number and then reverse the bytes.
While this approach is also linear in the
number of bits, it has the advantage of
being small and efficient of space and
time.
<D ; CLOSE FILES A RETURN TO C PM ^
W E 0
F
IMI
«
ROUTINt TO
FILL UP LAST RECORD •
WITH CP/M
EOF MARKS
ft
Mil
rfEOF : LXI
H , OB UF ♦! 28
; END OF BUFFER
XCHG
LHLD
OUT PT
;W HERE WE ARE
CALL
C PH L
; S A M E?
JZ
OUTBYT
;YES, WRITE LAST RECORD
MVI
A , • Z ' - 4 OH
;N0, GET A C PM EOF MARK
CALL
OUTBYT
;OUTPUT IT TO BUFFER
JMP
W EOF
;KEEP GOING
C L 0
S E F I L E
• i
•
SUBROUTINE
TO CLOSE FILES
•
ii
CLOSEFILE:
MVI
C.CLOSE
;CLOSE FUNCTION
LXI
D,DEST
CALL
B DOS
;CLOSE DESTINATION FILE
MVI
C.CLOSE
;C LOSE FUNCTION
LXI
D,SOURCE
CALL
B DOS
-.CLOSE SOURCE FILE
RIT
; ERROR
HANDLERS *
ERROR 1: LXI
D.MSSGl
JMP
ERRMSG
ERR0R2: LXI
D.MSSG2
JMP
ABORT
fcPROR3: LXI
D,MSSG3
JMP
ERRMSG
ERROR4: LXI
D,MSSG4
JMP
ABORT
ERROR5: LXI
D.MSSG5
JMP
ABORT
ERROR6: LXI
D.MSSG6
JMP
ERRMSG
ERROR7: LXI
D.MSSG7
ERRMSG: CALL
MESSAGE
JMP
FIN
;R ETUR N TO C PM
ABORT: CALL
MESSAGE
M E S S A C E
SUBROUTINE TO OUTPUT MESSAGE
MVI C, PR INT
CALL B DOS
RET
;PRINT FUNCTION
MSSGO
DB
•AlS- 8 to
DB
'by Ed Eli
MSSG1
DB
'Source fi
MSSG2
D3
'Read past
MSSG3
DB
'Directory
MSSG4
D3
'Disk full
MSSG5
DB
'Error in
MSSG6
DB
'No source
MSSG7
DB
'No destin
MSSG8
DB
'Conv ertinj
MSSG9
DB
'Done' ,CR,
DATA
BUFFERS: •
TEMP:
DS
1
TEMP2:
DS
1
DELIM
DS
1
FLAG:
DB
0
LOLC NT :
DB
0
DEST:
DS
33
OUTPT :
DW
OB UF
INPTR:
DW
IB UF ♦ 1 28
IB UF :
DS
128
CBUF :
DS
128
OLDSTK:
DS
2
DS
4 OH
NEW ST K:
EOU
$
TEMPORARY SAVE BYTE
ANOTHER ONE
ASC DELIMITER SAVE BYTE
SWITCH FOR QUOTED STRINGS
END OF LINE COUNT
DEST FILE FCB
OUT PUT POINTER
INPUT POINTER
INPUT BUFFER
OUTPUT BUFFER
OLD STACK POINTER
;STACK AREA
Page 48
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
265
AN IMPROVEMENT TO ZANT’S MODULAR
PROGRAMMING
Dear Suzanne:
The article on modular programming, authored by me and
published in DDJ #38, contains a program for appending
Applesoft programs. The published version of the program
works on tape-oriented systems and on systems using DOS
3.1, but will not work correctly on later versions of Apple’s
DOS.
The problem is caused by DOS 3.2 recalculating the chain
pointers for Applesoft statements each time a program is
loaded. The Append program must therefore be modified to
remove the instructions that perform this same function. A
listing of the modified program is enclosed.
Sincerely,
Robert F. Zant
Associate Professor of
Information Systems
:ASM
1000
1010
1020
1030
1040
1050
1060
1070
1080
1090
1100
1110
1120
1130
1140
1150
1160
1170
1180
1190
0308- 00 1200
0309- AD 08 03 1210
030C- DO 24 1220
030E- EE 08 03 1230
0311- A5 67 1240
0313- 8D 04 03 1250
0316- A5 68 1260
North Texas State University
Denton, Texas 96203
» APPEND FP
«
» ROUTINE TO APPEND
« APPLESOFT PROGRAMS
« ON THE APPLE II
K
« WRITTEN BY:
* ROBERT F. ZANT
»
» 01-07-80
*
« ASSEMBLED USING
* S-C ASSEMBLER II
«
BEGINL
»EQ
$67
BEGINH
.EG
$68
SAVEL
.EG
$304
SAVEH
.EG
$305
ft
.OR
$308
FLAG
.DA
«*-»
LDA
FLAG
BNE
SECOND
INC
FLAG
LDA
BEGINL
STA
SAVEL
LDA
BEGINH
0318-
8D
05
03
1270
STA
SAVEH
031B-
A0
00
1280
AGAIN
LDY
«$00
031D-
B1
67
1290
LDA
(BEGINL).Y
031F-
AA
1300
TAX
0320-
DO
06
1310
BNE
C0NT
0322-
C8
1320
INY
0323-
B1
67
1330
LDA
(BEGINL).Y
0325-
DO
04
1340
BNE
CONTI
0327-
60
1350
RTS
0328-
C8
1360
C0NT
INY
0329-
B1
67
1370
LDA
(BEGINL),Y
032B-
85
68
1380
CONTI
STA
BEGINH
032D-
86
67
1390
STX
BEGINL
032F-
4C
IB
03
1400
JMP
AGAIN
1410
«■
0332-
CE
08
03
1420
SECOND
DEC
FLAG
0335-
AD
04
03
1430
LDA
SAVEL
0338-
85
67
1440
STA
BEGINL
033A-
AD
05
03
1450
LDA
SAVEH
033D-
85
68
1460
STA
BEGINH
033F-
60
1470
RTS
1480
,EN
SYMBOL TABLE
BEGINL 0067 BEGINH 0068 SAVEL 0304
SAVEH 0305
C0NT 0328
FLAG 0308
CONTI 032B
AGAIN 031B
SECOND 0332
MAYBE JUST GALACTIC
Dear Dr. Dobb’s,
In DDJ # 43, Bud Gramer states that CP/M is “the only true
universal operating system.” Others have also made this statement.
Obviously a “universal” operating system must run on (almost) every¬
thing. Therefore CP/M (or anything else) will not be a universal
operating system until there are versions of it for the 6800, 6502, 6809,
Z-8000, 68000, etc., etc.
One approach to a really universal operating system would be to
pick a suitable high-level language such as C or PASCAL, and write
most of an operating system and the required utility programs in that
language. For each target computer, a small amount of assembly
language code would be needed for device drivers and interrupt
handlers. Most of the system would be the same (or nearly so) for all
computers.
While Mr. Gramer is “sick” of hearing about certain non-CP/M
systems, I am tired of the attitude of much of the microcomputing
community that the 8080, Z-80, and S-100 bus are the only things
that exist.
Sincerely, 5472 Playa Del Rey
Jim Howell San Jose, CA 95123
Number 46
266
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 55
A FEW THINGS . ..
Dear Suzanne,
I would like to inform your readers of an address correction
necessary for their responses to the article “Some Useful
Subroutines for a Z-80 Assembler” in DDJ #44.
I have received a significant response to that article, but
my mailing address has changed since the article was sub¬
mitted. For information concerning the subroutine library,
or for a copy of it, requests should be sent to: J. W. Carter,
3538 Deerwood, Memphis, TN 38111.
I would like to also add another opinion to the “adver¬
tising controversy.” I consider it unfortunate that Dr. Dobb’s
finds it necessary to include advertising in the publication.
Dr. Dobb’s is one of the few journals in this field with such
a select, and consequently devoted, audience. With no pretty
pictures and pie-in-the-sky dreams generated by ad¬
vertising, the reader receives only top-quality articles in the
field. Also authors, knowing a select audience exists are
encouraged to provide good quality manuscripts. With adver¬
tising entering the picture, I see this philosophy decaying; for
with advertising comes additional profit which is usually
passed on to the author. I would expect that, with advertising,
quality authors will tend to send manuscripts to other journals
which provide fiscal compensation.
I would rather see you raise the subscription rate and
include more of the material you have been publishing, than
see Dr. Dobb’s go the way cf the modem majority.
Sincerely, Memphis State University
John W. Carter Memphis, Tennessee 38152
Computer Systems Technology
REMARKS AS ENTRY POINTS
Dear DDJ:
Bruce Thompson’s letter in DDJ #45 states that jumping
to a remark in a program is a “serious error in programming
style,” but he fails to recognize that cramming as much active
code in a given amount of memory as possible is not the
only programming consideration. In many cases, readability
and ease of modification may be more important.
As a professional programmer, I know that memory is
usually cheaper than software, and have adopted a style that is
totally contrary to Mr. Thompson’s. In my programs, remarks
are defined as entry points either to in-line code or to subrou¬
tines. The advantage to this style is twofold: First, since you
know that a remark is an entry point, you will leave it alone
and won’t accidentally change it when performing modifica¬
tions to the program. You can add more code at the beginning
of a routine without having to shuffle line numbers. Second,
it is a tremendous aid in promoting readability to a program.
When you see the statement GOTO 1000, you can simply
look at the remark at line 1000 to see what happens when
you get there without having to wade through the code.
Not all entry points in my programs are remarks since
this would be wasteful in trivial cases, but all remarks are entry
points major logical procedures. Once it is understood that
this is the case, it adds a great deal of flexibility to the pro¬
gram.
Very Truly Yours, DATASMITH Micro Software Systems
Burks A. Smith 15501 West 109th St.
Lenexa, Kansas 66219
IMPROVEMENTS TO APPLE USER INTERFACE
Dear Suzanne,
I was very pleased to see the User Interface to the APPLE II
Program Renumbering in DDJ #42.
I found some errors and a possible error.
The errors:
1. Line 106 of the code is out of place. It should be between
lines 102 and 103. 2. At line 432 the S94B0 should be
94CO. 3. At line 551 on page 50 the code should read 20
58FC.
The possible error — it is at least an omission — is at line
563 and thereafter: the ASCII bytes for the headers. Perhaps
it is supposed to be obvious that they are not there. But a
beginner might be very perplexed, and certainly would be
dispma/ed at not having the program work properly. Below
is the correct code:
95 7E
C5
CE
9580
D4
C5
D2
A0
CC
C9
CE
C5
9588
A0
CE
D5
CD
C2
C5
D2
A0
9590
C4
C5
C6
Cl
D5
CC
D4
8D
9598
A0
A0
CE
C5
D7
A0
D3
D4
95A0
Cl
D2
D4
A0
AO
A0
A0
AO
95A8
A0
AO
A0
A0
B1
B0
B0
A0
95B0
A0
A0
A0
A0
CE
C5
D7
A0
95B8
C9
CE
C3
D2
C5
CD
C5
CE
95CO
D4
A0
A0
A0
A0
A0
B1
B0
95C8
B0
A0
A0
A0
A0
A0
D2
Cl
95DO
CE
C7
C5
A0
D3
D4
Cl
D2
95D8
D4
A0
A0
A0
A0
A0
A0
A0
95E0
A0
A0
B0
A0
A0
A0
A0
A0
95E8
D2
Cl
CE
C7
C5
A0
C5
CE
95FO
C4
A0
A0
A0
A0
A0
A0
A0
95F8
B6
B5
B5
B3
B5
A0
A0
A0
A few comments. If you are not going to use the program
with a disk (because you might not have one, for instance)
change each of the three bytes in line 549 to EA(NOP).
If you would like to have different default values for the
NEW START and NEW INCREMENT change the byte at
$9424 to the desired value. For example, I wanted my NEW
START to be Line 10 and my NEW INCREMENT 10 also.
I changed the value at $9424 to $0A. (I see no way of chang¬
ing one of those default values and not the other.) After I
made that change I then changed the ASCII data for the
headers so that ‘NEW START 10’ and ‘NEW INCREMENT
10’ are displayed.
That’s all. Hope this is helpful .
Yours, Rt 2 Box50A-l
Stephen E. Bach-AA4B Scottsville, VA 24590
Page 56
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 46
267
ON DIABLO
Dear Suzanne:
The enclosed program is based around a Z-80 USR call
that calculates the advance necessary for a Diablo printer to
print a string any desired width. The code has been expanded
somewhat to make it easier to install on other machines. The
last line of code could be replaced by a jump to whatever
location serves the same purpose. If the routine is used as is,
the defaults are a 72 character line with a 12 point type daisy
wheel.
Yours truly
L. Barker Chicago, IL
10 ' Variable printing for a Diablo
20 CLEAR MOO
30 DEF1NT 1,J
40 DEFUSR0 = &HA000
50 W = 41123! Width to be printed (in characters)
60 FOR 1= 0 TO 176
70 READ J
60 POKE 40960 Ul, J
90 NEXT
100 INPUT "Print what file (.rXT)";F$
110 INPUT "Print file what width ";J
120 IF J < 20 OR J > 132 GOTO 110
130 POKE W, J
140 INPUT "Advance ( = 120/point) ";1
150 IF 1=10 OH 1=12
THEN POKE W+1, 1
ELSE GOTO 140
loO OPEN "I",1, F$+".TXT"
170 LINE INPUT #1, A$
160 IF 1N5TR(A$,"=£ND") > 0 GOTO 220
190 IF LEN(Ai) < .75 • J
THEN LPH1NT A$;
ELSE A$ = USH0(A$)
200 LPR1NT
210 If NOT EOF(1) GOTO 170
220 CLOSE
230 END
240 ' Program loads at 0A000H (40960)
250 DATA 235, 70, 35, 94, 35, 6o, 33, 0, 0, 34,159,1o0, *4,161,100,213
260 DATA 58,163,160, 95, 64, 56,164,160,205,1*2,loO, 34,157,lo0,225, 5b
270 DATA 161,160,184, 40, 77,229, 60, 50,161,160,23/, 91,157,100,205,1*2
260 DATA 160, 14, *3,175, 24, 5,164, 56, 1,144, 6*. 2*7,106,2*5,2*/,lOo
290 DATA 235, 23, 13, 32,241, *1,237, 91,159,1o0, *4,159,160,16*,2*/, 62
300 DATA *5, 56,162,160,235,225,167, 40, 16, 14, 2/,203,105,IbO, 14, *1
310 DATA 205,165,160, 75,205,1o5,IbO,123, 50,1o2,lO0, 76, *5,205,1o5,loO
320 DATA 24,17*, 14, 27,205,165,160, 14, *1,203,165,loO, 56,164,160, 60
330 DATA 79,195,165,160, **, 0, 0,229, 14, 6, 41,22 /, 2*/ , 106,22/, /
340
DATA 46,
6, 25
, 46, 3,227, 35,22 1 , 13, 32,23*.204,201,144, 03,210
*50
DATA 75,
69,210
, 72, 10
*60
DATA 56,
0,207,2*0, 2, 40,249,121, 50, 1,20/,201
370
380
’ The last
data
Tine is to send register C to the line
printer.
390
400
• L1NEP:
LD
A,(PORT)
410
•
AND
2
420
■
JR
Z.LlNEP
430
i
LD
A, C
440
•
LD
(PQHT+1) ,A
450
RET
460
• URG
0CF00H ; modify as system
requires
4/0
• PORT:
A NEW LISP INTERPRETER
Dear Suzanne:
This is to announce availability of a new version of the
LISP interpreter which appeared in DDJ # 30. This program
is available from me on 8 inch, single density IBM format
CP/M diskette for $10.
GCLISP is a version of the Dr. Dobb’s LISP which has
been modified to run under CP/M (by addition of appro¬
priate drivers, has improved behavior when presented with user
program errors and can collect list garbage when memory is
exhausted. In addition, the code has been rearranged into a
slightly more logical format (all variables have been collected
at the end, data statements done more compactly) and initial¬
ization has been made more understandable. Provisions have
also been made for saving the system after defining new (inter¬
preted) functions.
CP/M features: The interpreter now sets up its own stack.
There is an assembly time option to use CP/M line buffered
input. The advantage of line buffered input is that LISP doesn’t
see the line until carriage return is typed, so the line can be
corrected during type-in. The assembly also generates an
equate for PAGSAV which is the number of pages for a CP/M
save command to allow using DEFINE to create a set of
functions and constants, then ctrl-C back to CP/M and save
the result. The interpreter uses the CP/M string type routine
to send error messages.
Improved control: In the original interpreter, errors in a
user program caused the interpreter to abort. In this version,
most errors result in a message and return to the EVAL-
QUOTE driver. In addition, EVAL checks for ctrl-D from
the terminal to abort long computations. The EVALQUOTE
driver now prompts for input with an underscore.
The interpreter has one new function, EXIT, of zero
arguments which returns control to CP/M.
Sincerely, 1522 Brockton Ave., Apt. 5
Darrel J. Van Buer Los Angeles, CA 90025
ELF TINY MONITOR
Dear Dr. Dobb’s:
Here’s an Elf Tiny Monitor for the Netronics Elf II that
has proven to be a big timesaver for me. The Elf II is virtually
identical to the 1802 based Elf introduced in a series of
Popular Science articles by RCA’s Joseph Weisbecker starting
in August 1976. The monitor presented here is an improve¬
ment over a similar program in the March 1977 issue because
it is shorter, performs the same functions and displays memory
location. I’d like to hear from anyone having a shorter pro¬
gram with equal features.
Load the following program starting at memory location
00HEX. Then turn off the RUN, LOAD, and Memory
Protect switches.
F8
ID
AF
EF
6C
30
1C
7B
3F
08
6C
AE
37
OC
8E
5F
EF
64
2F
3F
13
EE
C5
6C
C4
64
30
OC
30
1. To start execution at any memory location press the two
HEX keys that define the location and turn on the RUN
switch. The monitor writes into location 1DHEX, so user
programs must start after this.
2. To examine memory start execution at location 08HEX
according to instructions in (1) above, then press and
release the I key. The memory location (address) will
be displayed. Press and hold the I key to examine memory
contents, then release the key to display the next address.
Continue to press and release the I key to examine succes¬
sive memory addresses and contents.
3. To change memory start execution at location 07HEX and
follow the same initial sequence as in (2). The Q light will
come on indicating the memory may be altered. After the
memory location is displayed press the two HEX keys
that define the memory contents (data) to be entered
and press the I key. When the key is released the next
address will be displayed and the monitor is again ready
for input data.
4. To change modes turn off the RUN switch and begin anew.
Sincerely, 468 Velarde Street
R.C. Briggs Mountain View, CA 94041
Number 46
268
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 57
THE LOW DOWN ON TOP-DOWN
Dear Editor:
The letter by John R. Culleton, Jr. in DDJ #43 claims that
top-down programming is impossible in PASCAL (in con¬
trast to COBOL). I have used PASCAL heavily for five years,
and I always thought that on my best days I was working in
a top-down fashion, and quite successfully. The definition of
“top-down” must need clarifying, so here is mine.
“Top-down” programming is a method of designing and
writing programs which proceeds from the most general to the
most specific aspects of the problem to be solved. Typically,
the first step will be to write a skeleton program (or a narrative
outline) of what will be done. Subsequent steps, as many as
are necessary, provide detailed expansion of things that are
only outlined or named at a higher (previous) level. The task
is done when everything has been reduced to a form which can
be executed by a computer or which can be automatically
translated to such a form.
Niklaus Wirth calls this “stepwise refinement” and has
written two excellent books showing its use with PASCAL.
It can be used with any language. With none is it impossible
because it is almost independent of the qualities of the lan¬
guage used. One does not program in a language but into
a language.
Can Mr. Culleton define “top-down” in a way that makes
PASCAL unsuitable? And if so, can he defend the usefulness
of such a definition in the multi-lingual world we all inhabit?
Sincerely, 6440 Regent St.
David Rowland Oakland, Calif. 94618
(Continued from page 13)
be able to act as a front end processor, which
will handle all the communications chores for
a host machine. Once this is running, we can
see some very powerful and exciting possi¬
bilities for distributed processing!
The protocol currently used is a simple
“Aloha" type random access system. It has been
enhanced however and uses carrier sense and
priority acknowledgments. Since the current pro¬
tocol will probably be defunct by the time it is
published, here is the new version outline:
The Format
SYN
SYN
SOH
Destin
Call
6 bytes
Destin
Node
2 bytes
Origin
Call
6
Origin
Node
2
Service
Flag
1
(bit mapped)
Number
Flag
1
(bit mapped)
Length
Byte
1
(bit mapped)
Data
0
to 256 max
Checksum 2 bytes
The Protocol can almost be derived by
looking at the format of a packet. It is carrier
sensed, that is, stations don’t transmit if they
hear another station on the air. Priority ac¬
knowledged, i.e., if a station hears a packet
and the checksum is correct, it is presumed that
the destination station also got it correctly
and that an acknowledgment will be forth¬
coming. The transmission of a waiting packet
is delayed to allow the ack to go by unhinder¬
ed.
Where a station fails to get an ack to a
transmitted pac, it will try again, up to three
times. The interval between retries is random
to avoid two stations continually clobbering
each other’s pacs. All pacs are preceded by an
ASCII SYN (synch) byte and the ASCII Start
of Header characters. The Service flag is used
to indicate by setting a bit high (1) whether
the packet is an ack, a repeated pac or ack,
whether this is a file transfer, and ASCII or
binary data field, with a couple of bits to spare.
The bits are arranged as follows in this flag:
Bit 7 6 4 3 2 1 0
ARFB ????
Where A = Ack
R = Pac or Ack from the repeater
F = File transfer in progress
B = Data contains binary coded info
? = Spare for future use
Note: there was a terrific temptation to
rearrange the flags to read as B A R F,
but in software the ARFB series was easier.
The repeat flag is used to prevent a station from
receiving two packets if he hears both the
origin station and the destination. The
computer will respond to and keep the one
R flagged, and ignore the other. Don’t forget
the repeater transmitted pac will get there
after the original since it is store and forward.
The file flag is used to indicate that the re¬
ceiving station should file the packets sequen¬
tially and not allow other packets to intrude
in the file. You can imagine what getting a
“Hi Bob” pac would do if it was inserted in the
middle of a program I was receiving. Files are
also written to disk on the receiving com¬
puter. The binary flag is used when a file
(program etc.) is binary coded as this would
allow us to apply offset loading etc., to the file. It
will also allow a program to “come up running”
on a user’s machine.
The next flag in the sequence count is used
to keep packets composing a file in the right
order. It will also be used eventually to im¬
plement a virtual circuit where a certain
number of pacs will be allowed outstanding
without acks. This will allow for improved
throughput with an ACK to NUMBER (X)
arrangement. The length byte is obvious: it
simply tells the computer how long the packet
is. The only restriction is that packets cannot
have more than 256 bytes in that data field.
The last two bytes are the checksum which
is used to establish that the packet has been
received error free. This is currently done
in software but we expect to do it in hard¬
ware with the Fairchild 9401 CRC generator
checker chip in the final version.
Page 58
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E. Menlo Park, CA 94025
Number 46
269
Dr Dobbs (ouRNALof
COMPUTER
(Calisthenics Orthodontia
Running Light Without Overbyte
Number 47
August 1980
Volume 5, Issue 7
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
ZX65: Simulating a Micro
Richard M. Kruse
Clean Starts for COSMAC 1861 Video Output
Gary H. Price
Indirect Addressing for the 8080 and Z80
Anthony Skjellum
A Z-80 Circuit for the H-8
Ted T. Stowe
Harlie: A “No-Programming” Computer
J. L. Lawrence and Jay Sprenkle
...and, as always, even more
271
ZX65 : Simulating a Micro
BY RICHARD M. KRUSE
6221 Woodlow Drive
Wichita, KS 67220
ABSTRACT
This article gives complete details,
including source code, of an assembly
language program which functionally
simulates the operation of a 6502 micro¬
processor device using a Z80 based host
computer system. Under control of
ZX65, a wide variety of 6502 software
may be directly executed in any of
several modes. Useful for 6502 software
development as well as for its tutorial
value, ZX65 should prove to be a signifi¬
cant addition to the Z80 user’s software
library. Occupying only 4K Bytes of
system memory, ZX65 is sufficiently
flexible to be readily adapted to system
environments other than the one
described.
Having logged many hours of software
development work on my Z80-based
system, I recently decided that I was up
to a particular challenge: using my system
as a development tool for a totally
different microprocessor; specifically, the
6502. This decision, 1 must confess,
was not altogether based on a burning
lust for knowledge, but rather on a more
practical requirement: I had become
involved in the development of a 6502-
based device, and had no ready access to
a 6502 development system. 1 decided
that a simple cross-assembler wasn’t good
enough, and set out to write a 6502-to-
Z80 object code translator/simulator/
interpreter.
The program described here, which I
have dubbed ZX65, is the result of my
efforts to generate a software package to
perform this task. It is useful not only for
the intended purpose of software
development, but also for the rewarding
experience of exploring a whole new
field of good software written for a
processor other than one’s own.
ZX65 operates as an interpretive
simulator; that is, a simulated 6502 CPU
is maintained in system memory, and
each encountered 6502 instruction is
decoded and processed interpreter-
fashion to properly act upon the simula¬
ted CPU registers. The entire package
resides in just over 4K Bytes of high
system memory, leaving the remaining
portion, including the all-important (for
6502) base page, free for program and
data storage. Note that CP/M serves only
as a loader and is not used thereafter. In
fact, while the program loads normally
into CP/M’s Transient Program Area, it
immediately relocates itself into high
memory, overlaying both the CCP and
the BDOS portions of CP/M. The user
I/O linkages (CBIOS), however, remain
intact and are used by the package to
perform disk and console functions. The
functions which must be provided by the
system are a subset of those required by
CP/M and should thus be readily avail¬
able. These functions are all accessed via a
jump table within the interpreter and
thus can be readily changed to accom¬
modate different system requirements
(See Table 1). Parameters must be passed
to the drivers in register “C” (register
pair “BC” for item six) and data, if any,
is returned in the accumulator.
ZX65 is referred to as a package since
it includes three distinct function groups.
The first and largest is the interpreter/
simulator itself. The second group is an
elementary monitor providing the func¬
tions of memory examine and modify.
The third group consists of a self-
contained, elementary disk operating
system (DOS) (Note: ZX65 files are not
CP/M compatible). The normal configura¬
tion assumes a two-drive system, with
the system diskette on drive A, and all
internal disk access routed to drive B
(Modification for a single drive system
could easily be done, requiring the user
to switch diskettes after the package is
loaded). The package is written in
standard Zilog/Mostek source code and
is quite heavily commented. Much use
is made of the Z80’s special instructions
and index registers, and operation on an
8080 is definitely not possible without
extensive modification. Although the
commented listing should guide you
through the program’s operation without
too much trouble, a brief description of
the interpreter portion is in order. A
study of the small but powerful instruc¬
tion set of the 6502 will reveal certain
patterns in the op codes, as also occurs
with most other processors. The eight
“BRANCH ON CONDITION” codes, for
example, all have zero as a low-order
nybble, while the high-order portion is
always an odd value.
Another pattern, not so obvious, is
that every instruction having an odd-
valued op code uses multiple addressing
modes. These and other such patterns are
exploited by the program. Even so, much
of the code is devoted solely to decoding
the op code and transferring control to
the proper instruction processor. The
code beginning at “STEP” (line 241)
performs the initial decoding, and fully
decodes certain instructions such as
“RTI”, “JMP”, and a few others. In most
cases, decoding proceeds to a point where
the instruction is known to be part of a
group, such as the branch group described
above. In these cases, look-up tables are
used, but not always in the same way.
The branch group and the flag set/reset
group, for example, derive mask patterns
from the tables which are used for test¬
ing, setting, or resetting the condition
flags.
In the case of multiple addressing
mode instructions, however, the tables
serve an entirely different purpose. The
table contents are, in these instances,
decoded into addresses for indirect
jumps; first to the addressing mode
processors, and then to the actual instruc¬
tion processors. Each processor performs
its instruction as required. The “ADC”
instruction, as an example, causes a byte
of data to be fetched from memory or
from the object code, depending on the
addressing mode. After setting the Z80
carry flag to match the simulated 6502
carry flag, this data byte is added to the
value currently in the simulated accumu¬
lator, and the result is stored there. The
simulated carry flag is then updated to
again match the Z80 carry, and the
simulated sign, overflow, and zero flags
are set or reset according to the results
in the accumulator (In this case, the over¬
flow flag is set or reset according to a
logical exclusive “OR” of bits six and
seven). Considerable care has been given
to treatment of the flags, since Z80 flags
and their 6502 namesakes do not always
have the same meaning (Case in point:
the 6502 carry flag assumes a logical
Page 4
272
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
“NOT” BORROW meaning during
subtract and compare operations, while
the Z80 and most other common pro¬
cessors invert the carry flag internally
during these operations so that it repre¬
sents a “TRUE” BORROW; other flag
differences, for the most part, are more
subtle).
Finally, each individual processor is
responsible for exiting with codes for the
mnemonic, the addressing mode, and the
number of bytes occupied by the instruc¬
tion available for use by the “DISPLAY”
routine (line 173) to index into yet
another set of tables and retrieve the
ASCII messages for mnemonic and
addressing modes. Upon exiting the
instruction processors, the value stored in
“NEXT PROGRAM COUNTER” is up¬
dated, and control is passed back to the
COMMAND section where the operating
mode in effect determines whether to
display the updated CPU contents, and
whether or not to continue execution
with the next instruction.
Several distinct operating modes are
available, defined briefly as follows:
Single-Step Mode: One instruction is
decoded and executed. The console
then displays the address of the instruc¬
tion just executed (Current Program
Counter), the decoded instruction (Mne¬
monic and Operand), the state of all CPU
registers, and the address of the next
instruction to be executed (Next Program
Counter). Control is then returned to
the user.
Multi-Step Trace Mode: The user speci¬
fies up to 255 instructions to be executed
with the results displayed as above
following each step. This occurs at the
rate of approximately two instructions
per second. Control is returned to the
user after the required number of steps
have been executed and displayed.
Run-to-Breakpoint Mode: Instruc¬
tions are executed without display up to
and including the user-specified break¬
point. CPU registers are then displayed
as above and control is returned to the
user.
Free-Run Mode: Instructions are ex¬
ecuted with no display and no break¬
points. The console keyboard, however,
is monitored, and CPU contents are
displayed as above and control is returned
to the user at any point upon console
input.
The user may examine and modify
any or all CPU registers, including the
program counter, at any time that he
has control, without otherwise disturb¬
ing any operation in progress.
The 6502 “BRK” instruction (soft¬
ware interrupt) is handled through a
vector location, just as in a normal
system. Optionally, however, the BRK
instruction may be used (and is initial¬
ized) to return control to the user in the
same manner as the breakpoint mode des¬
cribed above. The BRK instruction and
breakpoint mode operate independently,
and both may be used in the same pro¬
gram. Additionally, up to five different
“user” subroutines may be called for
transfer of control to Z80 routines
(such as console I/O). These are in¬
voked by executing either a “JMP” or
“JSR” instruction to addresses 0000,
0001, 0002, 0003, and 0004 (HEX).
Control is passed via a jump table located
within the intepreter, which the user
may load with Z80 “JP” mstructions
to the desired subroutines. The sub¬
routines must be terminated in the nor¬
mal Z80 fashion by one of the “RET”
instructions. Note that the first two
entries in the table (JMP or JSR 0000,
0001 HEX) are initialized as console
input and output via the 6502 accumu¬
lator. Three parameters may be passed
to and from all user subroutines, as
outlined in Table 2. Table 3 lists the
locations of the BRK vector and the user
subroutine jump table.
Although the interpreter is quite vers¬
atile and all 6502 mstructions are handled
properly, there are some limitations to
its use. Perhaps the most important of
these is that, even in the “free-run”
mode, execution is quite slow compared
to an actual 6502 running at normal
clock speeds. No attempt has been
made to correlate execution times with
normal 6502 clock periods (this may,
in fact, be impossible due to the way
in which the system handles multiple ad¬
dressing modes). Therefore, programs
incorporating software timing loops will
not execute properly. Also, since the pac-
age was intended for software develop¬
ment, hardware interrupts are not sup¬
ported, and only a limited amount of
hardware interfacing can be performed
through the “user” subroutine calls.
Two program listings are included
here. One, “ZXLD” is located at the end
of this article. Its function is to boot
the main program from the CP/M Tran¬
sient Program Area to high memory.
The other listing is the interpreter itself,
assembled to reside from 6F00 to 7DFF
(HEX) in a 32K system.
Note that this leaves 512 bytes,
normally containing CBIOS, unaffected.
The program is not relocatable, so that
in order to run in a different memory
configuration, it will be necessary to
reassemble the source with a new value
in the “SIZE EQU XX” statement.
All other addresses are derived from this
value. If the object code is to be manu¬
ally loaded for the 32K system then
“ZXLD” must be loaded first, starting
at 0100 (HEX). Then start loading
ZX65 at 0110 (HEX), continuing until
the end. Finally, use the CP/M “SAVE”
command (SAVE 15 ZX65.COM) to
write the object code to disk. The pack¬
age can now be invoked by answering
“ZX65” to the CP/M prompt. If you
are reassembling the package, then you
should also reassemble the ZXLD routine
(modified for your system) so that you
have a .HEX file for each module. Then
load the package using DDT as follows:
DDT ZXLD.HEX
IZX65 .HEX
Rdisp
Where “disp” is the load offset value
required to load the object code from the
.HEX file at a different address than
that specified. (DDT will calculate
“disp” if you type “HI 10, ssss”, where
“ssss” is the actual starting address of
your program. DDT will respond with
the sum and difference of the two values,
and the difference will be the required
value “disp”.) Finally, save the object
code as directed above for manual load¬
ing.
To run the program, place the disk
with ZX65 .COM on drive A (this disk
should also have a copy of CP/M so that
the system can be restarted, if necessary,
without changing disks). Place the ZX65
data disk on drive B. Start CP/M and in¬
voke ZX65 by answering “ZX65” to the
CP/M input prompt. The system will
prompt you with a header and a “ > ”
symbol. You are now in the command
mode, and typing one of the command
codes (see Table 4) will cause the appro¬
priate action to occur. Note that if you
are using a disk not previously used for
ZX65 on the drive B, you will be unable
to use the ZX65 DOS functions until
you have initialized the disk. This is done
simply by typing “I”, at which point the
system will ask you to verify this request
with a “Y” or “N”. The reason for this
Number 47
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 5
273
(note this well) is that the “I” command
clears and initializes the directory on disk
B. This is the equivalent of the CP/M
command “ERA *.*” and must be
used with caution.
For those unwilling to type in a 4K
Byte program by hand, I will make the
package available on a standard 8 inch
IBM format, single side, single density
diskette (Sorry, I can’t handle any other
format!) at a nominal charge of $15
to cover time and material. Write to me
and specify your system memory size.
I will send a diskette containing both
source and object files assembled to re¬
side in high memory as described above,
as well as a copy of ZXLD. A command
summary, operating hints, and other
general information will be included on
the disk.
Finally, although this program has
been rather exhaustively tested with a
variety of 6502 software (both simple
and sophisticated) I cannot guarantee
it bug-free. I have included no copyright
notices of any kind, and I hope users will
feel free to copy, add, delete, and im¬
prove at will. (I would like to hear
of any major modifications... I may
want to include them myself!) As stated
at the outset, the package was developed
as a side benefit of another project, not
as a money maker, and if anyone else
finds it useful, so much the better.
Acknowledgments:
CP/M is a registered trademark of
Digital Research, Pacific Grove, CA.
While not specifically mentioned in
the text, I have relied heavily on the
information contained in the book
“6502 Assembly Language Program¬
ming” by Lance A. Leventhal (Os¬
borne/McGrow-Hill Inc., 1979).
Function Address
1. Test console input status 7A2EH
2. Get single character from console 7A2BH
3. Send single character to console 7A28H
4. Select disk drive (A or B) 7A34H
5. Home R/W head of selected drive 7A31H
6. Set disk transfer buffer address 7A3DH
7. Set sector number for disk access 7A37H
8. Set track number for disk access 7A3AH
9. Read one sector from selected
drive 7A40H
10. Write one sector to selected drive 7A43H
Table 1: Functions which ZX65 requires of
the host system, and their locations within
the interpreter.
6502 Register Passed as
Accumulator
X Index
Y Index
Table 2: 6502/Z80 Parameter
subroutines.
Z80 Register
Accumulator
B Register
C Register
passing for user
_
Description
Address of vector or
jump instruction
BRK Vector
7A55H
User 0
7A46H
User 1
7A49H
User 2
7A4CH
User 3
7A4FH
User 4
7A52H
Table 3: Locations for ‘BRK’
jump table.
vector and user
Command Function
C CPU register display and modify.
D Directory display of ZX6S files
on disk B.
Format: FILNAM.TYP
LOAD ADDRESS # RECORDS
E Examine a block of memory.
System will prompt for starting
address and number of bytes.
G Go to 6502 program per Current
Program Counter and execute
without display (free-run).
I Initialize a fresh disk on drive B.
(Must be formatted.) System will
prompt for verification.
K Kill a ZX6S file on drive B. Simi¬
lar to CP/M ERA. System will
prompt for file name.
L Load a ZX65 file from disk B.
System will prompt for file name.
M Memory substitution. View
sequential memory locations and
update if desired. System will
prompt for address. Mode will
continue in effect until a ‘. ’
(period) is typed.
R Load and run a ZX65 file from
disk B, starting at the address
specified in the directory. (Must
be an executable 6502 program.)
System will prompt for file name.
S Save a ZX6S file on disk B.
System will prompt for file name,
starting address, and number of
bytes.
T Trace several 6502 instructions
with display following each step.
System will prompt for desired
number of steps.
SPACE Single-step command. System
will execute one 6502 instruction,
display the results, and stop.
Table 4: A command summary for
ZX65 ( in alphabetical order).
LISTING
CD
CL
z
O
LU
b-
CD
z
LU
<1
«X
b-
z
ID
CJ
<L
r-J
Ll
O
X
►—«
CL
z
CO
b-
CD
o
CO
b-
LU
<L
3
O
CO
CO
CO
LlI
IL
<r
S
LU
X
CL
CL
z
z
•D
CO
LU
o
x
_1
LU
CU
z
©
o
IU
cr.
ID
CO
F-
CL
LL
Lj
CJ
b-
X
CJ
CJ
cj
CL
CL
CL
o
CL
Hi
<_•
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Page 10
278
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
I .A.I .I JJ .=
q “no programming
BY J. L. LAWRENCE AND JAY SPRENKLE
Computer Science Dept. Software Lab I 1
University of Missouri —Rolla 1
Rolla, Missouri 65401 __
It was with much interest and skepticism that the authors
read the article “Build a Self-Learning No-programming Com¬
puter with your Microprocessor” by Klaus Holtz in DDJ #33.
The article describes a computer which requires no program¬
ming, is educated almost like a human child, and is relatively
inexpensive. Applications suggested'for this new computer in¬
clude language translation, a typewriter which refuses to type
incorrectly spelled words, unbreakable secret codes, and others
which are currently difficult to implement. All of this is
claimed to be achievable with no programming!
The article’s author describes briefly the theory behind the
proposed computer as “Knowledge Processing and Infinite
Dimensional Networks.” It would be nice to have a reference
for such an amazing theory, if a reference does exist. Rather
than repeat the theory here, we merely pause to mention it.
As Holtz points out, understanding of the theory is not neces¬
sary to implement his ideas.
Figure 1.
1ST REM
20 REM * HARLIE •
30 REM • *
40 REM ••••••••*••••**•••••••••••••
80 DIM I$(72).M1(2),M9(2),M5(2000,1),T$(72),T(72),W(72)
90 DIM AjUlOT.l)
100 N= 2000!M£(N,0)=-9999iM5(N,l) = -9999
110 M=10»iA5(M,0)=-9999iA5(M.1)=-9999
120 1 CHR$(26)
130 I TAB(23),"-"
140 I TAB(23) i "I H. A. R. L. I. E. I"
1J0 I TAB (23 ) , "."
160 111 TAB(19),"I AM A SELF-LEARNING COMPUTER"!IiI
170 1iIi1$=""iINPUT "> ",I$
180 IF I$="*ST0P" THEN STOP
181 IF I$=“»MEM” THEN 245
182 IF I$="*CLEAR" THEN 246
190 I9=LEN(I*)iIF 19=0 THEN 170
200 IF It(I9,I9)<> " " THEN 230iREM GET RID OF TRAILING BLANKS
210 I*=I$(1,I9-1)
220 GOTO 180
230 GOSUB 250
240 GOTO 170
245 GOSUB 1310IGOT0 170
246 GOSUB 1500iGOTO 170
250 REM SENTENCE ENCODING ROUTINE
260 IF I$(l,l)=”»" THEN S=1 ELSE S =0
270 IF S=1 THEN LS=I$(2,LENU$))
280 L9=LEN(1$) i IF I$(L9,L9)=”?" THEN 0=1 ELSE 0=0iREM WAS IT OUESTION
290 IF Q=1 THEN I$=I*(1,L9-1)
300 IF I$(1,2) = "A»" THEN Q.21REM IS IT AN ANSWER
305 IF 0=2 THEN S«11 REM ALWAYS STORE ANSWERS
310 IF 002 THEN 330
320 I4>=I$ (3. LEN (1$))
330 L9=LEN(I$)iJ9=1iW1=-1iF2=0
340 I $=""1 FOR I=J9 TO L9
350 IF I$(I,I)=" " THEN 390
360 T$=T$i1$(1,I)
370 NEXT I
380 GOTO 440
390 J9=1*1
400 GOSUB 1040i REM CONVERT T$ TO T
410 P9=-liG0SUB 8901 REM SEE IF I KNOW IT ALREADY
420 W1=W1111W(W1)=AiIF F> 0 THEN F2=F
430 GOTO 340
440 P9=-l1GOSUB 1040■GOSUB 890
450 W1=W1U iW(Wl )=Ai IF F >0 THEN F2-F
460 FOR 1=0 TO WliT(I)=W(I)iNEXT I
470 T(Wl«l)i32
480 ?9=-2iGOSUB 890iREM ADD SENTENCE
490 IF P>0 THEN F2=F
500 IF 0=1 AND F< 2 THEN A9=AiREM ADDRESS OF LAST OUESTION
510 IF 0 =0 THEN 6101 REM NOT A OUESTION OR ANSWER
520 IF F2=0 OR F2=l THEN 560
530 IF F2=2 THEN I$="»”» I DON'T KNOW •***"
540 IF F2=3 THEN I$= ”»••• more STORAGE REQUESTED ***•"
550 GOTO 650
560 GOSUB 700iREM GET ANSWER
570 IF F=0 THEN 5901 REM 1 KNOW THE ANSWER
580 GOTO 610
590 GOSUB 1190
600 GOTO 650
610 IF F=0 THEN !$."•••• I KNEW THAT ••••"
620 IF F*1 THEN I$."**»« I WILL REMEMBER THAT •••••
630 F2-F
640- GOTO 530
650 I IS
690 RETURN
700 REM ASSOCIATIVE NETWORK ROUTINE
710 F=JP
720 IF 0=1 THEN 750i REM ANSWER NOT SET
730 Ml(1)=A9iMl(2)=A|REM PUT IN NEW ANSWER TO OUESTION
740" GOTO 760
750'Ml(l)=AiREM PUT IN OUESTION
760 4=0-
7706 G=A5(A,0)1 P=A5(A,1)iM9(1)=GiM9(2)“PiREM FETCH MEMORY WORD
7806 IF THEN 8301 REM ALL ZERO
7906 IF G=M1(1) THEN 8601REM OUESTION-POINTER
800 A=A»1
810 IF A5(A,0)< >-9999 THEN 770
820F=3iGOTO 880!REM MORE MEMORY
830 IF 0=2 THEN 850! REM ANSWER KEY SET
840 F=2iG0T0 860iR£M I DON'T KNOW
850^A5(A,in*Ml (1) 1 A5</^jl )=M1 (2)1 F-PGOTO 880iR£M STORE MATRIX REGISTER
860 IF 0=2 THEN 850iREM ANSWER KEY SET
870 A=M9(2)
880 RETURN
890 REM SERIAL NETWORK — FIGURE 2
900 A=0i Ml (2) = P91 P5= -11 F=0
Number 47
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 11
279
Figure 2.
91* P5-P5*l «i»l (1 )-T(P5) i REM GST NEXT INPUT CHAR
92*C-M5(A,/).P=M5(A,l)iM9(l).GiM9(2)-PiR£M FETCH MEMORY WORD
93/ IF G •/ THEN 98 /i REM WORD IS ALL ZERO
94/ IF G-Ml(l) AND P>M(2) THEN 1/1/iREM WORD"MATRIX REGISTER
95*A=A*liREM INCREMENT ADDRESS
96* IF M$(A,0)<> *9999 THEN 92/iREM END OF STORAGE?
97* F^JiGOTO 10V
98* IF S=1 THEN 1/0/. REM STORAGE ENABLED
99*F=2lGOTO 1/3/
1/// F=1iM5(A,/)=M1(1)iM 5(A,1)=M1(2)'RE» STORE MATRIX REG IN MEmORY
inner Ml(2)=AiREM LOAD ADDRESS INTO POINTER
lerzer if mi (i) <> 32 then 910 .rem gate=end code
1D3B- RETURN
latter rem convert t$ to t
L0"5* L=LEN(T$)
106/ FOR 1=1 TO LiT(I-1)=ASC(T$(I,I))iNEXT I
1/7* T(L) = 32
1080- RETURN
109/ REM RETRIEVAL ROUTINE — FIGURE 3
110/ P5=-1,T$=""
1110-G=M5(A,/)iP=M5(A,1)iM9(i)=GiM9(2)=PiREM FETCH MEMORY WORD
U2*P5=P5 *llT(P5)=G
1130'IF P=P9 THEN 115/1REM POINTER = *(l)
1140 A=PiGOTO 111/
1150" FOR I=P5 TO * STEP -1
116 O’ TS=TS*CHR$(T(I))
1171* NEXT I
118* RETURN
119* REM RETRIEVE A SENTENCE INTO 1$
120*Wl=-liI$=""iP9=-l
1210 K9=M5(A,1)'REM SKIP END OF SENTENCE MARKERS
1220 Wl=Wl+l i T(W1 )=M_5(K9,/)
123*IF M5(K9,l)=-2 THEN 1250
124* K9=M5(K9,1)iGOTO 122/
125 * FOR 1=W1 TO / STEP -liW(Wl-l)»Ttl)iNEXT I
126* FOR J =/ TO W1
127* A=W(J)iGOSUB I/ 9 / 1 REM RETRIEVE WORD
128*I*.I$+T$
129* NEXT J
13/* RETURN
131/ REM PRINT OUT MASS MEMORY
132/ P5=/
133/ I P5.TAB(l/),M5(P5,0),TAB(2/).M5(P5.1).TAB(30),
134/ IF M5(P5,/) > 31 AND M5(P5,/)< 128 THEN 1 CHR$(M5(P5.0)) ELSE I
135 / ?5=F5M
136 / IF M 5 (P 5 ,/)> =1 THEN 133 /
137 / P 5 =*| I "ASSOCIATIVE MEMORY"
138/ I P5.TAB(i/),A5(P5,/),TAB(2/),A5(P5,1),TAB(30)
139 / P5=P5U
14// IF A 5 (P 5,/)>=1 THEN 138 / ELSE RETURN
15// M5(/,/)=/iM5l/.l)=/iA5(/,*)=/iA5(/ I l)=/'
151/ «5(l.*)V M 5(l .1)"/aA5(1,/)=/iA5(i,i)=*
152/ RETURN
Being fully aware of the philosophical problems and impli¬
cations of computer “learning” (and wishing to protect our
future as programmers!), we decided to implement the pro¬
posed machine. Instead of using hardware to actually build the
machine, we simulated the machine in software. Figure 1 is a
listing of the program in Northstar BASIC which we ran on an
Imsai 8080. Furthermore, we have run the same program on
an Apple II and an 8080 with CP/M and Microsoft BASIC. The
code can be vastly improved upon, but the implementation
was intended to reproduce the hardware description as faith¬
fully as possible. In the terminology of the original article,
lines 890-1080 represent the Serial Network Routine, lines
1090-1180 represent the Retrieval Routine, and lines 700-
880 represent the Associative Network Routine. The rest of
the code is fairly obvious and is used to enhance the I/O. See
figure 6 of the original article for further clarification. As for
main variables, array A5 represents the associative network
memory, array M5 represents the serial network memory, Ml
is the matrix register, and M9 is the memory word.
I H. A. R. L. I. E. i
I AM A SELF-LEARNING
> «JLL?
.... j DON'T KNOW *•••
^ A*314-364-2831
•••• I WILL REMEMBER THAT •♦**
> *UMR?
.... j DON'T KNOW ***•
~3 A»UNIV. OF M0. ROLLA
♦♦♦♦ I WILL REMEMBER THAT ***•
> *JCL?
.... 1 DON'T KNOW *•**
> A*JOB CONTROL LANGUAGE
***• I WILL REMEMBER THAT ****
> UMR?
UNIV. OF MO.-ROLLA
> JLL?
314-364-2831
> “STOP
STOP IN LINE 181
READY
Operation of H.A.R.L.I.E. is straightforward. Figure 2 illus¬
trates a sample run. Referring to figure 2, “>” is the prompt
character indicating that H.A.R.L.I.E. is expecting a response
from you. All user responses are underlined for clarity. To use
H.A.R.L.I.E., the user merely types in the request/response at
the keyboard. Any response preceded by turns on the
storage flag and causes whatever was typed to be placed in
the serial network memory (array M5) if it is not already
there. Any response which ends with “?” is a question which
H.A.R.L.I.E. will answer if he can. If H.A.R.L.I.E. doesn’t
know the answer to the question, he will respond with
“**** I don’t know ****”, as figure 2 shows. After an un¬
successful query, H.A.R.L.I.E. expects you to supply the cor¬
rect answer although it is not necessary. Preceding the re¬
sponse with “A*” causes H.A.R.L.I.E. to remember the cor¬
rect response the next time the appropriate question is asked.
This is the way in which H.A.R.L.I.E. “learns.”
Figure 3.
memory location
memory contents
pointer
end of question marker
end of word marker
end of sentence marker
ASCII equivalent
mm
Page 1 2
280
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
17
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ASSOCIATIVE
MEMORY
0-*-
5
24
2
53 — 77
“JOB CONTROL IS DIFFICULT” were later added to the
serial network memory. Only “IS DIFFICULT” would require
additional storage, Holtz claims. Note that spaces are not
stored except as “end of word” markers.
Well, H.A.R.L.I.E. works as advertised but . . . he’s not
practical. HA.R.L.I.E. suffers from two major problems. First
of all, before H.A.R.L.I.E. can answer any question, he must
have been asked that exact question before and have received
an answer. Furthermore, H.A.R.L.I.E. requires that the ques¬
tion be asked in exactly the same way each time. Hence,
H.A.R.L.I.E. can’t think or reason; he merely repeats what has
been stored.
►memory location
►pointer to answer
►pointer to questions
Figure 3 shows the contents of memory after the dialogue
of figure 2 has occurred; refer to the original article for a
description of how to follow the pointers. The point to be
made here is to illustrate what Holtz means when he claims
that the more information stored, the less storage required to
store additional information. From figure 2, note that “JLL”
and a phone number was entered. Later, “JCL” and “JOB
CONTROL LANGUAGE” were also entered. Looking at fig¬
ure 3, the “J” is stored only once. Suppose the sentence
Secondly, H.A.R.L.I.E. is intolerably slow. Getting answers
out of HA.R.L.I.E. can take an extremely long time and is
highly dependent upon the order in which he first “learned”
what he “knows.” (If you have read “When HARLIE was
One,” you’ll recall that this imagined machine could answer
any question, but the answer might not come in the ques¬
tioner’s lifetime. Hence, the authors chose the name
“H.A.R.L.I.E.”) Many things could be done to speed up
H.A.R.L.I.E., such as programming in machine code or even
using hardware, but this won’t help very much for very long.
The problem lies in the extensive use of pointers which any
experienced programmer knows is costly in terms of speed.
Hence, improvements could be made but they aren’t worth the
extra effort. Note that the original article specified the use of
tape for mass storage, because it’s cheap, which would further
degrade the speed of H.A.R.L.I.E.
In conclusion, H.A.R.L.I.E. does work but he is highly im¬
practical. Users won’t be dumping accumulated “knowledge”
from one tape to another as Holtz envisions, nor will know¬
ledge be sorted in all-knowing Super Computers with this
particular design, which accomplishes the task of fact retrieval
in a very awkward and inefficient manner. Much better tech¬
niques exist that are currently operative in many database sys¬
tems. After reading Holtz’s article and this one, the reader will
realize that both are meant to be taken with a healthy sense
of humor and a large block of salt!
(Author’s Note: H.A.R.L.I.E. is taken from the science fiction
book “When HARLIE was One” by David Gerrold.)
Number 47
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 13
281
CLEAN 5TART5 FOR
\ C05MAC I8bl
1 DEO OU T F U T
Sunnyvale, CA 94086
The 1861 low-resolution video chip is
a versatile adjunct to the 1802 Cosmac
microprocessor, but the interrupt soft¬
ware required for frame formatting typ¬
ically slows program execution by about
a factor of two. This overhead can some¬
times be alleviated by enabling and dis¬
abling the 1861 under software control,
as is done, for example, by Netronics
ELF II TINY BASIC when using the
1861 for character output. A clean start
is not assured, however, on the first frame
following an 1861 re-enable unless spe¬
cial precautions are taken. The 1861 DIS¬
PLAY STATUS line provides a means,
as will be described, by which a re-enable
can be synchronized with the interrupt
and DMA requests to the 1802 through
which the video frame is produced.
The 1861 DISPLAY STATUS line is
set low twice per frame, once during the
last four horizontal scans preceding the
display window and again during the last
four horizontal scans of the display. The
interrupt request by which the display-
refresh routine is entered is set during the
last half of the first of these two
STATUS-low periods. Sync signals are
output by the 1861 even while disabled
in order to maintain frame synchroniza¬
tion. Thus, if the 1861 is re-enabled with¬
in the display window (as can occur with
ELF II TINY BASIC), the initial series, or
partial series, of DMA requests following
the enable will be received during execu¬
tion of code outside the display-refresh
routine. Such an occurrence is accom¬
panied by a flash of “garbage” on the dis¬
play screen.
The code given in Listings 1 and 2 a-
voids such bad frames by assuring that
the 1861 is enabled outside the display
window. DISPLAY STATUS is assumed
to be connected to 1802 flag line No. 1
(active low), and DISPLAY ON and DIS¬
PLAY OFF are assumed to be connected
to the decoded N lines set by the 1802
I/O instructions IN,1 (69) and OUT,l
(61), respectively, as in the ELF II. Regis¬
ter 2 is assumed to be pointing to an a¬
vailable memory location for the I/O byte
transfers associated with the IN and OUT
instructions (e.g., the next location on
the top of the stack). Two versions of the
routine are given. That in Listing 1 per¬
tains to the case in which DISPLAY
STATUS is directly connected to the
1802 flag line. The version given in
Listing 2 is for the ELF II with I/O-
monitor board installed. In this system,
the 1861 DISPLAY STATUS and SYNC
signals are ORed to generate the flag in¬
put to the 1802.
Listing 1. Basic 1861 reactivation routine.
Label Instruction
WAIT1 B1
WAIT1
WAIT2 BN1
WAIT 2
SEX,2
SEX,2
LOOP NOP
NOP
DEC,2
IN,1
OUT,l
B1
LOOP
IN,1
Listing 2. 1861 reactivation routine for
ELF II with l/O-monitor board installed.
Label Instruction
WAIT1 B1
WAIT1
B1
WAIT1
WAIT 2 BN1
WAIT2
SEX,2
LOOP NOP
NOP
DEC,2
IN,1
OUT,l
B1
LOOP
IN,1
The initial tests of DISPLAY STATUS
preceding LOOP in the listings allow
entry to the loop, the timing of which is
critical, only on initiation of the STATUS
signal. With only the first B1 in the
WAIT1 loop in Listing 2, about 99 per¬
cent of the starts will be clean, but two
tests in sequence are necessary in this case
to prevent dropping through the hold on
the SYNC pulse. In both the Listing 1
and Listing 2 versions of the routine,
synchronization of the 1861 timing with
the 1802 instruction fetch/execute cycle
will be reestablished during the holds if
it has been disrupted (e.g., by any 3-cycle
instructions closely preceding entry into
the routine). Once the final loop has been
entered, the 1861 is enabled only during
a series of brief windows between possi¬
ble DMA-request bursts. Should the
STATUS signal be that preceding the dis¬
play window, the onset of the interrupt
request is caught by one of these enable
windows, and an ordinary display frame
is generated by the interrupt-service rou¬
tine. Upon exit from the interrupt-service
routine, STATUS is high, and the 1861 is
permanently (until the next disable) en¬
abled as the loop finally is exited. Should
the STATUS signal be that preceding the
end of the display window, however, no
interrupt is encountered during its dura¬
tion, and the loop keeps the 1861 dis¬
abled during the periods that it otherwise
would be initiating DMA action. Once the
inhibited frame has passed, as indicated
by STATUS going high, the loop is
exited, and the 1861 finally is enabled
permanently. The timing of the signal
lines involved is shown in Figure 1.
Gary Price is a physicist at SRI who is
learning about microprocessors from his
ELF II. He has done a hand-compilation
for the 1802 of Dick Duda’s Othello pro¬
gram from its original BASIC, and he
would be happy to share this program on
a Netronics-format tape. - SR
Page 14
282
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
Figure 1. Timing of some 1861 signals and 1802 responses.
1802 instruction cycles (each 8 clock cycles)
M I i l l i i i l| M tl I I I I 1 I I I I I I | I II | l l I ) l M I I l l I I I I M I I I I l l i I II I I i i I
DISPLAY STATUS
~l_
SYNC
“U U U-LT-—U
INTERRUPT REQUEST
I - 1 interrupt response cycle
DMA REQUEST
I I I I I It It 1 I II II 1—i — I I I I I I I I I I It I I I I I I I M-
DMA cycles
Notes:
1. Start of display window only
2. End of display window only
Number 47
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 15
283
The PCNET Project has operated a
bulletin board system* in the San Fran¬
cisco Bay Area for about two years.
The system we’re running now is the
Apple Bulletin Board System from Peri¬
pherals Unlimited. In late May/early
June of ’80 our ABBS experienced a
(for me) novel problem; a person or
persons would call the system, give a
CB-like ‘handle’ instead of a name
during logon, and then leave messages
making free use of all the well known
anglo-saxon expletives.
Other bulletin board systems in the
area experienced similar behavior by
someone using the same handle. Systems
operators discussed the matter, and we
all agreed that the commercial time¬
sharing service procedure of requiring
login via password would solve the pro¬
blem, but would sharply restrict the pre¬
set free access policy of BBS systems.
We rejected this approach as putting
too much of a damper on easy BBS
access. Meanwhile back at the system
the bad guys had grown more disagree¬
able, threatening to crash the system
as well as leaving offensive messages.
I was intrigued by the problem of devis-
sing BBS security programs which would
detect and discourage abusive behavior,
but which would not be too much of a
burden for (or better still not even be
visible to) ordinary users. I coded up
some security extensions to the ABBS
which seem to have been effective against
the bad guys; the number of offensive
messages has dropped to near zero and
there have been no system crashes in spite
of several threats to that effect.
Two security measures seem to be
particularly useful. Both are straight¬
forward technically, but one involves
some interesting psychology.
THE DIRTY WORD FILTER
This is a string parsing subroutine that
detects any use of offensive words or
phrases. The Dirty Word Filter is used
on names submitted by users during the
logon procedure as well as on almost all
other strings sent by the user while he
is on the system. If a dirty word or
phrase is detected, the phone connection
is immediately broken.
THE UNDESIRABLES LIST
The kind of person who gets his
kicks from this sort of thing seems to
have an ego involvement with the
‘handle’ he uses. He becomes the focus
of attention with the added advantage
of anonymity; “the mysterious DIRTY
HARRY strikes again!”. The undesir¬
ables list contains the names used on all
objectionable messages. Whenever such a
name is used on entry, the system breaks
the phone connection. If new aliases
are used, they are easily added to the list.
It’s hard to build up a reputation as a
mysterious evil doer if you have to keep
changing your name.
Some systems (e.g., ABBS) have the
unfortunate property that if crashed
the remote user is given full control of
the system with the ability to alter the
system program and do other anti¬
social things. Proper attention to detail
in writing the system software can make
a provoked crash very unlikely; there is
a hardware fix that can make it impos¬
sible. It’s called a watchdog timer. The
concept is fairly simple; a hardware
monostable multivibrator is built that can
be reset by an output signal from the
system computer. A circuit of this kind is
easily built using a 555 timer and a few
other parts; the whole thing should cost
less than $5. The timer is set to time out
in 1 to 5 seconds. A subsroutine is added
to the BBS system that restarts the timer
each time it is entered; this subroutine
is called from enough places in the BBS
so that the timer is always reset before
it times out. If the system crashes for
any reason the subroutine doesn’t get
called and the timer times out and hangs
up the phone.
If all else fails your friendly local
telephone company is prepared to assist
in preventing your computer from being
embarrassed by bad language. They have
equipment which, with modest coopera¬
tion on the part of the BBS operator,
can trace the number from which the
dirty data was sent. Use of obscene words
over the telephone turns out to be illegal,
even if the languge is ASCII. So all you
obscene data callers out there had best
be careful. Your next visitor may be a
cop with a bunch of printouts showing
just what was sent from your phone and
when.
I’ll be happy to share the full details
of all my system security measures with
other BBS operators. I’m not going to
put them in this article; one doesn’t
provide detailed plans of the bank vault
in an article on how to foil bank robbers.
Write me care of DDJ and I’ll arrange
to supply you with the details.
You can write to Dave Caulkins at
PCNET, P.O. Box E, Menlo Park, CA
94025.
* (See The Electric Phone Book
on p.21 of the June/July DDJ for a list
of them.)
Page 16
284
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
PROGRAMMI
PASTIMES
AND
PLEASURES
©1980, BY CHARLES WETHERELL
Dataflow Computers
There is a tremendous range in speed
between the fastest and the slowest
computer in common use today. I don’t
know what the slowest commercial com¬
puter is (perhaps we should have a write-
in contest?), but an 8-bit addition in
5 microseconds seems reasonable. This
rate is still about the same as the addition
speed of the IBM 1401 that I learned to
program on back in 1964, so really this
may not be so slow.
But it is not nearly fast enough for
scientists who need answers to big prob¬
lems. They often use a Cray-1, perhaps
the fastest computer available on the
market right now. A Cray-1 can do a
64-bit addition in about 15 nanoseconds.
Ignoring questions about carries, the
Cray-1 also does eight times as much
work. But this is not the whole story. The
Cray-1 sometimes can do five operations
at once. So the additions could possibly
go on 13,335 times as fast on a Cray-1 as
on the microprocessor chip you bought at
your local computer store.
How much of a difference is a factor
of 13,335? Assume that some program
takes exactly one minute on the Cray-1.
The microprocessor would take almost
1-1/3 weeks! And if the Cray-1 program
took one hour, the micro would take
slightly more than 1 Vi years! Since
Cray-l’s are commonly used for time-
dependent problems like weather predic¬
tion, a delay of a year and a half in turn¬
around could make a forecast of rain for
tomorrow fairly useless.
Money and Technology
Speed is not the whole story, of
course. Our hypothetical micro might sell
for a couple of dollars and I could likely
package it with memory and power for
well under $100 in a useful configuration.
The Cray-1 has a price tag of $5 mega¬
bucks. (Admittedly, the Cray-1 does have
much more memory, but memory is
relatively cheap.) The price ratio is
50,000 to 1, about three times my
optimistic estimate of the speed ratio
and perhaps ten times a more conserva¬
tive speed ratio. Scientists pay heavily
for the speed they need. And now many
scientists are calling for gigaflop comput¬
ers capable of one billion floating point
operations a second. Imagine what these
giants will cost.
There is hope, though. The cover
article of Scientific American for May,
1980, describes how superconducting
computers built from Josephson junc¬
tions might be built. A prediction of
about one nanosecond per instruction is
also made, exactly what is needed for a
gigaflop execution rate. But the article
demonstrates, albeit indirectly, why a
Josephson computer (and the Cray-1)
will cost so much. To build the superfast
giant, whole new areas of technology and
engineering have to be developed,
improved, or refined. All the learning and
research cost money. In high technology
manufacturing, serial number 1 of a new
product is always expensive (remember
the first transistor radios and hand calcu¬
lators). After a hundred, a thousand, or a
million items have been sold, the research
cost can be spread out and drop to dollars
or pennies per item.
The villain here is the necessity to use
components employing the most ad¬
vanced and expensive technology. What
if the $2 microcomputers could somehow
be connected together to solve the big
problems using only reasonably standard
technology, particularly using no super¬
fast components? Then the supercomput¬
er might not require an appropriation
from Congress to buy.
An Army of Ants
How can a $2 micro beat a Cray-1?
By enlisting a lot of friends. Assume that
I can buy a reasonably cheap micro¬
processor that will do a 64-bit add in one
microsecond. If 1,000 of these micros all
run continuously on the same problem,
they will average an operation per nano¬
second. More realistically, if 5,000 micros
each operate only 20% of the time
because of scheduling and communica¬
tion delays, the whole group will still
average one nanosecond per operation.
Metaphorically, an army of ants might be
able to crash through the jungle as fast
as an elephant if the ants can get
organized.
Dataflow graphs are a way to organize
the ants. Consider a typical calculation
like (x 2 + y 2 )/(x 2 - y 2 ). In a normal
computer, this would take at least five
steps. But look at the dataflow graph:
Now it is clear that two computers could
cooperate and do the calculation in three
steps by sharing the work. If you remem¬
ber that scientific calculations are much
more elaborate than our simple example
and that thousands of similar elements
have parallel computations done on them,
you can see that there is plenty of oppor¬
tunity for parallel operation. Conven¬
tional computers hide this possible speed-
Page 18
Dr Dobb’s Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 47
285
up because instructions must be executed
sequentially even though the dataflow
graph shows there is no dependence
between two instructions. In fact, many
programs could have entire loops or sub¬
programs executed in parallel if their host
computers could do the job.
A New Architecture
A dataflow computer has five main
components: instruction memory, data
memory, arbitration network, distribu¬
tion network, and a battery of processors.
In a conventional computer, instructions
sit passively, waiting for the CPU to call
them for execution. On a dataflow
machine, each instruction takes an active
part in the computation. An instruction
waits for all of its operands to be ready;
when they are, the instruction signals the
arbitration network that it is ready for
execution. The arbitration network packs
the data and the instruction together and
ships the package to a free processor.
When the processor is through executing
the instruction, the results are shipped
back through the distribution network to
any instructions waiting. In the graph
above, the output from the left-hand
square instruction would be passed to
both the add and the subtract.
We can notice a number of facts about
a dataflow machine. First, many instruc¬
tions may be clamoring for execution at
the same time; it is the responsibility of
the arbitration network to sort out the
chaos. There is no requirement, by the
way, that the instructions be processed
in order of readiness. Second, processors
do not have to be synchronized at all
nor need they all have the same capabili¬
ties. Data gets back to waiting instruc¬
tions whenever the processor gets
finished. The arbitration network must
make sure instructions go only to proces¬
sors that can execute them. Third, this
scheme will work only if on average
there are several thousand instructions
ready to execute at one time and if
bottlenecks, when only one or two
instructions are ready, occur only rarely.
Dataflow relies more than most architec¬
tures on good statistical behavior in
programs, a property likely in scientific
computations. Finally, the data store will
be used to hold large data aggregates like
records and arrays. This part of the
system will require considerable
engineering because it will have to be
smarter than the average memory.
Dataflow is the idea of Jack Dennis
at MIT and right now researchers around
the world are working on ways to build
dataflow machines. The promise of
growing a fast, large computer out of
many slow, cheap components intrigues
scientists, computer engineers, and
administrators who pay for computers.
Here’s hoping for success.
Number 47
286
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 19
Z - 80 “~—
Circuit for the
H-8
BY TED T. STOWE
704 Harbor Road
Bricktown, NJ 08723
Thought you might be interested in a Z-80 circuit for the
H-8 computer. I have had this circuit running for several
months and have had only one minor problem, and that is that
I had to go to CP/M for a Z-80 assembler as the Heath disk
operating system is strictly 8080.1 find in retrospect that my
only gain with HDOS is faster instruction execution time,
which created a problem with system utilities which sampled
the real-time clock. However, the latest release of HDOS
(ver 1.5) which is intended for the H-89 (Z-80) and H-8
(8080), has been updated in that area (both use the same clock
speed and essentially the same monitor).
To enable the front panel single-step to function, it is
necessary to remove IC108 and tie pin 8 to pin 11. This circuit
has been operating with all of the Heath H-8 boards and the
only problem to date that has popped up is with the latest
version of the Heath 16K board, part number 85-2197-1.
A minor conflict with the bank-enable exists that I haven’t,
as yet, had the time/inclination to resolve. If any problems/
questions arise I will answer any correspondence.
(continued on next page)
Page 20
Dr Dobb s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
287
eftT
Number 47
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 21
if
inDIRECT ADDRESSIfie
FOR THE 8080 AflD 280
BY ANTHONY SKJELLUM
1695 Shenandoah Road
San Marino, CA 91108
Abstract
The 8080 and Z80 microprocessors
do not provide indirect addressing modes
for all instructions. This article, a re¬
sponse to a previous one dealing with
indirect CALLs for the 6502, deals with
the implementation of indirect addressing
in software. Three techniques are ex¬
plored: the “ mini-program, ” as discussed
in the 6502 article, the self-modifying
subroutine and the self-modifying macro
instruction. These techniques are applied
to various instructions which lack the
indirect mode. As well, the use of the one
byte RST calls is suggested as a means of
accessing the indirection routines in a fast
manner. Finally, a specific example
dealing with the Z80 indexed addressing
mode is provided. The many listings are
provided to act as a tutorial and an
impetus to the reader to use the methods
suggested in future software develop¬
ment.
After reading Kenneth Skier’s article
“Indirect Addressing for the 6502,”
in the January issue of Byte, I compiled
a set of routines to handle indirect
addressing for some of the cases where it
is not available for the 8080 and Z80
microprocessors. While the particular case
of indirect subroutine CALLs handled
by Mr. Skier is easier to implemenet on
8080-type processors, several other oper¬
ations are not available with the indirect
addressing mode. The particular aspects
dealt with here are (1) the implementa¬
tion of the indirect CALLs as mentioned
above, (2) the lack of indirect mode for
memory loads and stores of 16 bit
registers where the direct mode is pro¬
vided for, (3) indirect addressing for
input-output (I/O) instructions on the
8080 specifically, and (4) indirect mode
for indexed addressing on the Z80.
Besides the several general examples,
one specific programing example has
also been included to give the reader
an idea of how the techniques discussed
here might actually be applied. As well,
the use of RST CALLs is included to sug¬
gest a fast access technique for some of
the self-modifying routines included
below.
Indirect Calls
Creating indirect mode for subroutine
CALLs was one of the main points dis¬
cussed in the previously mentioned article
dealing with the 6502. This procedure
is very easy to accomplish on the 8080
and Z80 microcomputers without the
use of dedicated Random Access Memory
locations as suggested by Mr. Skier for
the 6502. Listing la provides a trivial
routine to allow this procedure. The
routine ICALL is CALLed by the main
program with the HL register pair set up
with the address of the target subroutine,
i.e., the subroutine to be executed in¬
directly. The main program’s CALL
places the correct return address of the
hardware stack where it remains until
the target subroutine performs some sort
of return instruction (assuming that the
stack is not tampered with). The PCHL
(Program counter := HL) instruction
directs the program flow to the target
subroutine by executing an indirect jump
to the address contained in the HL regis¬
ter pair. This effects an indirect CALLing
system.
However, suppose the subroutine re¬
quires data of some sort to be sent in the
HL register pair (as is ofter the case). In
such a situation this technique will not
suffice. A modified version of Listing
la (in Listing lb) uses a dedicated word of
memory to store the value of HL to be
passed to the target routine. ICALL2
takes HL and places it on the stack above
the main program’s return address. It
then loads HL with the contents of the
location MEMW, which contains the cor¬
rect data, and executes a RET instruc¬
tion. The RET fetches the top address off
the stack which is the target subroutine’s
address. Execution continues at the target
routine as before and the additional stack
usage will not affect the main program’s
return address, also on the stack.
Indirect Register Addressing
In the 8080-type microprocessors,
the accumulator is provided with indirect
addressing over the BC, DE, and HL regis¬
ter pairs. In fact, the eight bit general pur¬
pose registers B, C, D, E, H, and L may
even participate in indirect addressing
referred to the HL register pair (i.e.,
MOV B,M does B:=(HL)). However, no
such mode is provided for the sixteen bit
register pairs such as HL which IS pro¬
vided with direct addressing. We will now
consider several aspects of creating indi¬
rect addressing for the 8080 and Z80.
Listing Ha illustrates the routine LHLI
which performs an indirect load of HL
from the address pointed to by HL ini¬
tially. Note that this code is not self¬
modifying but that it uses a 4 byte buffer
called SCRATCH which must reside in
Random Access Memory. The function
of this routine may not be openly ob¬
vious. What’s being done is that the
routine effectively creates a “mini¬
program” in the SCRATCH memory
which consists of an LHLD opcode (load
HL direct) a two byte operand field for
the LHLD instruction and a RET instruc¬
tion to give control back to the main pro¬
gram. (To get a visual idea of the “mini¬
program,” see Figure 1.)
memory address SCRATCH.
OPCODE FIELD:
One or two bytes in length.
OPERAND FIELD:
One or two bytes in length.
RETURN INSTRUCTION:
One byte in length.
FIGURE I. The general form of
a "mini-program" as presented in
this article. Note that Z80 in¬
structions may use two byte
opcode fields. Two byte operand
fields occur more often for both
Z80 and 8080 instructions.
Page 22
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
289
It is the modification of the operand field
of the LHLD instruction which allows us
to create the indirect load. The LHLI
routine stores the address provided on
entry into the operand field. Then it
executes the “mini-program” with a
jump (JMP) instruction. The HL pair is
loaded with the contents of the provided
address and then the program RETums to
the address found on the top of the hard¬
ware stack. Of course, this is the return
address to the main program and execu¬
tion continues there.
Listing lib contains the routine $LHLI
which performs the same function as
LHLI in Listing Ila. However, because it
uses the self-modifying technique, it is
shorter and faster than LHLI. Essentially,
the “mini-program” that was executed
through LHLI is done in-line. The first
SHLD (store HL direct) stores the address
which the main program provided. It is
stored into the operand field of the fol¬
lowing LHLD instruction which proceeds
to load HL with the contents of the given
memory address. The self-modifying ver¬
sion looks more inviting than its predeces¬
sor. However, it should be noted that this
technique is not available when programs
are stored in Read Only Memory. Addi¬
tionally, as pointed out by Mr. Skier, the
method can be volatile and potentially
cause disastrous results to a program if
used incorrectly. Finally, Listing lie is the
macro for $LHLI. It provides a means for
direct in-line use of the self-modifying
routine directly within the main program.
Sometimes, it is also advantageous to
perform indirect stores into memory. In
this case, it is not practical to have the
register pair also serve as the indirection
pointer (i.e., when would (HL):=HL be
useful?). Instead the DE pair may be used
as in listings Ilia, Illb, and IIIc, and Illd
(the macro for SSHLID). The routine
SHLIDE takes six bytes of program mem¬
ory while the method employing the
“mini-program” in SCRATCH is about
three times as long and consequently
slower. Analogous routines are possible
for the Z80 type load-store direct in¬
structions (LDED, LSPD, SBCD, etc.)
where the two byte opcode must be ac¬
counted for when creating the SCRATCH
“mini-program” as well as in the self¬
modifying versions.
Indirection For Input-Output
The 8080’s I/O instructions are limited
to direct mode with accumulator ad¬
dressing. That is, the ports referenced are
always constants and the data is either
sent from the A register or loaded into it
depending whether the instruction is an
OUT or an IN. Once again it is possible to
circumvent this with either self-modifying
code or the SCRATCH technique which
has been used above. Listing IVa presents
IND, a routine which creates a “mini¬
program” and executes it in a fashion
analogous to LHLI. IND expects the port
to input from the accumulator and loads
the accumulator with the returned value.
Listing IVb presents SIND which is the
self-modifying version of IND while
Listing IVc is the macro version of IND
for in-line use in the main program.
(Once again the same caution must apply
to the use of the self-modifying code.)
Listing Va contains OUTD, a routine to
effect indirect output instructions for the
8080. Again the SCRATCH buffer tech¬
nique is used. This time, data is sent in
the B register and the accumulator con¬
tains the port number. Listing Vb is the
self-modifying version $OUTD while
Listing Vc is the macro routine, OUTD,
which is analogous to Listing IVc. It is
important to note that Z80 users have no
need for this type of coding for indirect
I/O since it is provided in the Z80’s in¬
struction set. Any of the general purpose
registers or the accumulator may be used
for the data pointer while the C register
holds the port number. Special block
input and output instructions (OUTI,
INIR, etc.) are also provided.
Z80 Indirect Indexing Mode
The Z80 provides eight bit signed
two’s complement indexed addressing on
its IX and IY registers. The indexing
modes involve many varieties of opera¬
tions, but the basic drawback in some
cases is that the index is fixed. However,
it is possible to create routines similar to
those previously presented to alleviate
this problem. Fortunately, the index off¬
set byte is always the third byte of the
index instruction no matter which one it
is. Therefore, one example of a “mini¬
program” and self-modifying code should
serve as examples for the reader’s own
possible use. Listing Via, VIb and Vic all
perform an indexed MOV instruction
while the second is self-modifying and
the latter is the macro instruction. The
following section is a specfic example
which uses the macro IXMOV of Listing
Vic to illustrate how these “software
generated” indirect addressing modes
may be used to increase program effi¬
ciency.
A Specific Example
Listing Vila contains a portion of a
LIFE program that I wrote some time
ago. The routine MCOUNT was designed
to lookup the number of neighbors of
each life cell on the video display screen
which it uses and to save the number in a
one kilobyte storage area for later access
in determining the fate of the next LIFE
“generation.” The point of including this
routine here is that it uses the indexed
register MOV instructions of the Z80 to
access the different neighbors’ memory
locations relative to the cell under inspec¬
tion. However, each of the eight checks
requires an indexed MOV followed by a
CALL (the CELL macro expansions) to
the neighbor tally routine, CHECK (see
Listing Vile). It would be preferable to
write a loop which performs each loca¬
tion check in eight iterations. However,
this is not possible with the use of the
direct indexed addressing mode. Thus, it
is necessary to incorporate the macro in¬
struction sequence, IXMOV, into the pro¬
gram in order to make the routine more
efficient. This allows the neighbor checks
to be done in an eight count loop instead
of as a series of eight MOV-CALL (CELL
macro) sequences. Listing Vllb demon¬
strates the recoding of the NCOUNT
function to include the IXMOV macro
sequence and an inner loop. The recoded
version, SNCONT, uses about twenty-
two less bytes than the previous routine,
NCOUNT. As hoped, the routine utilizing
the indirect mode macro is more efficient
than its predecessor. (Note that Listing
Vile contains references used by both
NCOUNT and SNCONT.)
Using Restart Vectors
I’d like to make one last point about
the use of the self-modifying routines.
They are usually short enough to use in
one of the 8080 and Z80 type RST vec¬
tors located in page zero. If a particular
type of instruction is called frequently by
the main program, it may pay off in
terms of throughput and memory to uti¬
lize a RST call to execute the special in¬
direct instruction. RST instructions per¬
form one byte CALLs, and at a saving of
two bytes per CALL, this may save mem¬
ory space where short, or help speed up a
routine which is inherently time related.
Conclusion
In this article the implementation of
indirect addressing modes for certain
8080 and Z80 instructions has been dis¬
cussed. This included indirect memory
addressing for sixteen bit registers (specif¬
ically HL), indirect I/O addressing, indi¬
rect subroutine referencing and indirect
indexed addressing for the Z80’s IX and
IY registers. As well, the use of the 8080-
type RST vectors was touched on as a
possible code and time saver in imple¬
menting these ideas.
BIBLIOGRAPHY
1. Skier, Kenneth, “Indirect Addressing
for the 6502,” BYTE, January 1980,
pp. 118, 119.
Number 47
290
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 23
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
291
Number 47 Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025 Page 25
292
LISTING Hid. : LISTING IVb
Page 26
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
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Number 47
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Page 40
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Dr. Dobb s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
0001 ; LOADER
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ti R R U R -I* — ij 00 0
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THE END
Page 42
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
307
RULES NOT ALWA YS MADE TO BE BROKEN
Dear Editor:
If any of your readers are thinking about hanging a dot¬
matrix line printer onto their microcomputer system, I have a
friendly warning to pass on to them. “Pay close attention to
your manufacturer’s recommendations, or know the risk
you’re taking if you ignore them.”
For example, North Star recommends the Anadex DP-8000
connected to the parallel interface of their Horizon. But com¬
paring printer specs, I chose to save a few bucks by building a
Heath H14 line printer for the serial interface.
I saved some money at $625.00 plus shipping, plus an
additional $82.98 at Heathkit Electronic Center in Seattle
when the H14 flunked its initial power-on tests. They replaced
two defective CMOS IC’s and repaired three open foil breaks
in the five volt supply on the PC board at no charge, but they
detected erroneous installation of seven transistors. (Consider¬
ing the obvious textual errors in the documentation, which
would you believe—the text, or the pictorials? I guessed wrong
and followed the pictorial. Customer error!)
My WH14 printer tested perfectly at 4800 baud under
HDOS in Seattle. It went ape at 4800 baud on the Horizon
after I got it home. A quick phone call to my friendly Horizon
dealer divulged the fact that North Star DOS does not test
for handshaking signals! (The Heath manual advises to run
no faster than 110 baud without handshaking.)
So now I have a 110 baud line printer dawdling along
while the 4MHZ Z-80A and I are twiddling our respective
thumbs! Does anybody out there want to trade an in-warranty
Anadex DP-8000 printer for an in-warranty Heath WH14 plus
some extra cash?
Sincerely, 4807 Fifteenth Ave. S.E.
John R. Dye Lacey, WA 98503
GROWING PAINS IN THE SOFTWARE MARKET
Dear Suzanne;
On seeing my letter published in the April, 1980 issue,
I realize that my expression of my frustration at the marketing
methods of the CP/M products could easily be misconstrued
as condemning these products or their marketer. This was not
my intent and I would like to publically retract the poorly
written letter.
I have every reason to believe that the packages offered
by Lifeboat Associates are very valuable items. I believe that
Lifeboat does a skilled job developing some of these pro¬
ducts for wider use.
My problem is that as a relative newcomer to data proces¬
sing with a great perceived need for business systems not yet
available, I have devoted at least half my working efforts for
several years in this direction. I find that to implement a new
complex package that I need more support than I am able to
obtain by telephone during limited daytime hours from New
York City. I have scoured the dealers of the Northwestern
United States and occasionally elsewhere and can find virtually
no one who can demonstrate the CP/M software packages
in operation. When I have inquired why this obviously de¬
sirable material is not offered, they tell me that they have to
purchase these from Lifeboat at list price and that they can
not afford to do this. Hence they stick with the sytems which
are promoted through dealerships.
I believe that both the CP/M producers and Lifeboat
Associates have the full right to market their product anyway
they please. However, for this product to serve the needs to a
person like myself who is capable and willing to pay for them,
they have to offer some type of distributed customer service
perhaps comparable to Sears or Penneys. Both of these latter
companies have customer service departments in my city. I
can go and get almost any type of assistance in operating or
implementing any product ordered through the catalog. Soft¬
ware packages are complex items especially when run on exist¬
ing machinery.
The purpose of my comment was to alert the marketers
to the fact that their valuable material was not serviceable
in the hands of a remote user.
Most sincerely,
Robert C. Luckey, M.D. Richland, WA
Dr. Luckey is entirely correct in his claim that many soft¬
ware products-as well as hardware products-are not a-
dequately serviced once they are bought. It was once ex¬
cusable because of the “newness” of the micro industry;
however, that excuse no longer rings true. Vendors of both
hardware and software products can and must increase the
way they respond to the buyer after the product is sold. If
not, they will simply go under. Only the best deserve to
survive in this market; and that is not only a function of those
who sell the best product, but of those who maintain their
product and serve the customer after the product is sold.
Automobile manufacturers who had no warranties or follow-
through, once the auto was sold, would quickly go out of
business because nobody would buy their products. It should
be this way with software and hardware. Dr. Dobb’s en¬
courages you to send both your praise and horror stories to
us. - SR
Number 47
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Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 43
ANIMAL
Dear Suzanne,
Regarding Charles Wetherell’s ‘famous programs’ in DDJ
#42, the smallest program that will run the longest time is
something like
HERE JUMP HERE
which will run for as long as you let it, besides being portable
to any computer I know of.
As far as ‘virus’ programs, I know of one story: a large
development center of a large computer manufacturer (I
won’t tell you which) had a game called ‘Animal’ in which
one had to guess which animal the program was talking about
by making questions to the program and analyzing the answers.
What the player did not know, however, was that while the
game was being played, the program accessed the user’s di¬
rectory and copied itself into every file (in this machine files
are composed of elements, so one can have multiple elements
in a file) it could get hold of. In a while, virtually every file
of that computer had its own copy of ‘Animal,’ and I was
told that the management held several secret meetings to
find a way of getting rid of the ‘animal’ without ever acknow¬
ledging that it existed!
Albertus Caesar Chalfont St. Peter
22 The Paddock Bucks SL9 QJQ
England
CORRECTION
Dear Suzanne Rodriguez,
I’m afraid I made a few mistakes in the letter published in
DDJ #45. The BASIC demonstration program should have
read —
145 PRINT
150 PRINT “X” = ”;CY,C\256
160 PRINT “Y = ”;CY,C MOD 256
Also, in the article on page 36 there is a reference to a routine
on track zero to initialize the 16 ports at 0CF00H. This routine
is on the disks from OSI, it is not on the disks referred to in
the article. The problem then is not that the ports are over¬
written, it is that they are never initialized to begin with.
A late but happy Easter.
Yours truly,
L. Barker
MORE ON KEYPLUS
Dear DDJ:
We would like to thank Lt. Ronald Nicol for his favorable
review of our Keyplus Integrated Utility Package for the
TRS-80 in DDJ #45. However, there are two points that need
clarification.
Lt. Nicol states “The documentation that comes with the
software is excellent with the exception that the chart of
graphic symbols is inaccurate.” Not true; we triple-checked
and the chart is 100% accurate.
Later on Lt. Nicol remarks that all utilities, even ones not
being used, must be resident in memory. The Lt. believes this
to be a drawback. In all fairness, it should be pointed out that
the tape loads in just 20 seconds and requires less than 800
bytes of space; furthermore, utilities may be enabled or dis¬
abled in just two key strokes! Isn’t this better than fooling
around with several tapes each with a separate utility on it?
One final point, a disk-based version of Keyplus is avail¬
able for $19.95. Disk Keyplus contains several enhancements.
Sincerely, SJW, Inc.
Steven Wexler P.O. Box 438
Huntingdon Valley, PA 19006
TINY-C ON PHIDECK
Dear DDJ:
The May Special Issue — The C Programming Language-
struck a responsive cord at this location. A few of your readers
might be interested to know that I have recently been licensed
by Mr. Gibson to market an implementation of tiny-c (TM)
for Digital Group Phideck systems. For the sum of $25 I will
supply a tape and documentation. No overlays are used, so
any version of Phimon can use tiny-c. A minimum of 26K,
including the 2K set aside for Phimon, is necessary. The cas¬
sette tape has been prepared with a Phideck readable copy of
tiny-c on one side and an audio copy on the flip side in case
the Phideck version cannot be loaded. I also include several
tiny-c utilities which I have developed. All of this, following
Mr. Gibson’s lead in the tiny-c Owners Manual, is accom¬
panied by many pages of documentation.
Any prospective user is urged to purchase the Owners
Manual from tiny-c associates. Anyone wishing to know more
details can write to me.
Yours truly, DIGITAL GROUP Phideck Version
Charles Hemminger 20 Harrison Ave.
Northampton, MA 01060
A DIFFERENT ERROR
10 REM ** THIS PROGRAM IS TO POINT OUT A PROBLEM **
20 PRINT “COMPUTERS NEVER MAKE MISTAKES”
30 LET X = X + 1
40 IF X = 10 THEN 60
50 GOTO 10
60 REM ** LETS STOP PRINTNG THIS JUNK **
70 END
I thought the problems with this program were:
1. LETS should be LET’S
2. X was never initialized
not that transfers were made to REM statements in two places.
Sincerely, 400 N. River Rd., #904
Mark D. Senn West Lafayette, IN 47906
Chicago, II.
Dear Dr. Dobb s:
Bruce Thomson’s program in DDJ #45:
Page 44
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 47
309
Dr. DoBB'S JoURNALof
COMPUTER
(Calisthenics Orthodontia
Running Light Without Overbyte
Number 48
September 1980
Volume 5, Issue 8
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
A Runtime Library for the Small c Compiler
Ron Cain
Hardcopy Device Driver Programs for CP/M
Steve Willoughby
A Note on 6502 Indirect Addressing
W.D. Maurer
The Love Program
Gary Gaugler
311
RUNTIME LIBRARY
BY RON CAIN
811 Eleventh Ave.
Redwood City, Ca. 94063
COMPILER
The May 1980 issue of Dr. Dobb’s Journal (DDJ #45), highlighting the C Programming Language, was one of
the most popular issues ever. Foremost in popularity among the articles was “A Small C Compiler for the 8080's,
by Ron Cain. Due to popular demand, we are now publishing Cain’s “Runtime Library for the Small C Compiler. ’
Page 4
312
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
The small C compiler for 8080’s published in DDJ #45,
made reference to a runtime library. Although the listing of
that runtime library did not appear in that issue due to the
sheer mass of code of the compiler itself, there has been suffi¬
cient demand (and there is now sufficient room) for it.
Actually, the library consists of two distinct modules of
code. It contains: (1) the arithmetic and logical routines
which are called from the code generated by the compiler, and
(2) the I/O routines likely to be called by the user.
The two modules are largely independent of one another,
and it is conceivable you might choose to put them in separate
files. Such a split would be exceedingly easy to accomplish.
All the routines from “ccgchar” to “cccmpbcde” are the
arithmetic and logical routines. All the routines after that are
related to I/O.
Perhaps it would be helpful to discuss how the compiler
generates code to use the arithmetic and logical routines
within the library. Suppose you have the following piece of
code:
int ram word;
char rambyte;
samp (value) int value; (return (ramword / value - rambyte);)
The compiler would generate the following code:
samp:
LHLD ramword
PUSH H
LXI H, 4
DAD SP
CALL ccgint
POP D
CALL ccdiv
PUSH H
LDA rambyte
CALL ccsxt
POP D
CALL ccsub
RET
ramword: DS 2
rambyte: DS 1
You will notice that, as I mentioned in the previous article,
the compiler is very cautious in its use of registers. For all
the binary operators, it always gets the first operand into the
primary register (HL), puts it on the stack, gets the second
operand (also into HL), pops the first operand off the stack
into the secondary register (DE), and then does the operation.
In the example above, it first evaluates “ramword” into
HL with a simple 16-bit load. Seeing the “ / ”, it pushes
HL onto the stack, and evaluates “value” into HL. Since
“value” is defined as an argument passed to this routine,
the compiler has to generate the address of where “value”
is on the stack. At the time of the call to “samp”, the stack
would have looked like:
SP + 0 —> LSB of return address
SP + 1 -> MSB of return address
SP + 2 -> LSB of ‘Value”
SP + 3 -> MSB of ‘Value”
However, after pushing “ramword”, the stack would have
looked like:
SP + 0 — > LSB of ramword
SP + 1 — > MSB of ramword
SP + 2 — > LSB of return address
SP + 3 — > MSB of return address
SP + 4 -> LSB of‘Value”
SP + 5 -> MSB of ‘Value”
Therefore, the pair of lines of code:
LXI H, 4
DAD SP
would generate the address of “value” in HL. To get the con¬
tents of ‘Value”, the compiler generates a call into the runtime
library to the routine “ccgint”. Looking at the listing of
“ccgint” (the third routine in the library), you’ll see it loads
the HL register with the 16-bit integer pointed to by HL.
Therefore, upon return from “ccgint”, the compiler knows HL
contains the contents of “value”. Since it now has both
operands for the operation, it pops into DE the operand for
“ramword” it previously put on the stack, and calls another
library routine “CCdiv” to perform the divide. The routine
“ccdiv” returns the quotient in HL, which the compiler
dutifully puts on the stack upon seeing the “ — ”. Since
“rambyte” is defined as an 8- bit entity, the compiler evalu¬
ates it with a simple 8-bit load intruciton. Since it also
assumes all operands to be 16 bits, it sign extends “rambyte”
into a full 16-bit value in HL by calling the library routine
“ccsxt”. Nearly done then, the compiler pops the previously
evaluated quotient off the stack, calls another routine to do
the subtract, and exits. Any routine calling the routine “samp”
would then have the results expected in the HL register.
It’s really not very complicated, and after looking at it
for a moment you can see why the compiler can be so simple.
All binary operators work in the same fashion. The few
utility routines (like “ccgchar”and “ccgint”) work in a very
predictable way, and inevitably return a 16-bit value in HL.
In fact, the routine “ccgint” is the compiler’s universal routine
for indirect references, which you see in code like:
int * ptr;
samp () return ***** ptr;
which would generate:
CALL ccgint
CALL ccgint
CALL ccgint
CALL ccgint
CALL ccgint
RET
ptr: DS 2
Naturally, I would expect that many people would like to
improve and expand their own runtime libraries. One simple
improvement noticed by Walt Bilofsky (and since implemen¬
ted in my own version of the compiler), lies in the fact that all
the binary library routines (ccdiv, ccsub, ccxor, etc.) are
always invoked from the generated code by:
POP D
CALL ccxxxx
The obvious move is to modify the compiler to not gener¬
ate the “POP D” instruction, and to modify the library
routines to contain their own “POP D” instruction. Let’s
trace such a modification down as an exercise:
In the case of the divide operator, look at the listing of the
compiler in the other issue. In the C routine “heir 9( )”,
you’ll see where it parses the “/” character and performs the
division. Where you see the two lines of code:
pop();
div();
simply remove the “pop()”, and the compiler will no longer
output the “POP D” instruction prior to the “CALL ccdiv”.
Then, in the routine “ccdiv”in the library, simply insert the
three lines of code:
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 5
313
POP B lunstack return address
POP D ;unstack operand into DE
PUSH B prestack return address
at the beginning, and you will have improved your version of
the compiler. The number of “POP Destructions generated
is considerable, and the compiled code will be made smaller
by this simple modification, However, shorter code is not
necessarily faster code. The extra “POP B” and “PUSH B”
instructions in the library routine represent 32-bits worth
of memory reference, and memory reference instructions are
the slowest. So you can make your own version “optimized”
(I use the term loosely) either for speed or for space.
Another improvement to the compiler can be made to the
routine “ccpchar”. If you’ll glance at the routine “putstk”
in the compiler listing, you’ll notice it has the line of code:
if (typeobj==cchar) call (“ccpchar”);
else call (“ccpint”);
Anytime the compiler wishes to store a single character
at the address contained in DE, it calls “ccpchar”. Looking
at the routine “ccpchar” in the runtime library, you’ll notice
it consists of the code:
ccpchar: MOV A, L
STAX D
RET
Those familiar with the 8080 will realize the call instruction
takes more room than the routine itself. Therefore, an obvious
improvement for both code compaction as well as speed
would be to make the compiler drop this code inline. Changing
that one line of code in “putstk” to:
if (typeobj==cchar) ol (“MOV A, L”): ol (“STAX D”) ; }
else call (“ccpint”);
would accomplish this with a minimum of effort.
In fact, any or all of the routines in the library could be
executed inline if desired simply by finding where the com¬
piler generates the instruction “call(“ccxxxx”)” and replacing
that with calls to the routine “ol” for all the necessary instruc¬
tions. The compiler began life putting the code inline, and
only after it became obvious which way the wind was blowing
(toward another 8K memory board) did I change it to generate
this threaded code.
Other mods to the runtime library might include the addi¬
tion of floating-point routines. I am in the process of adding
Charles Falconer’s floating-point routines to my own library.
In time, either he or I will probably make the compiler smart
enough to generate calls to these routines to handle floating¬
point numbers. Until then, I will simply call them as external
routines from the program I write. Perhaps you have math
routines in ROM, or an AMD 9511 chip, or some other favor¬
ite set of math routines. The runtime library is as good a place
as any to put them if you expect to use them frequently.
String comparers, string movers, random number generators;
these are all good candidates for the libarary.
Apart from the arithmetic and logical routines, I mentioned
the runtime libarary also contains the I/O routines. My version
supports Polymorphic’s 8810/8813 disk operating system.
I know this is not the most popular choice, and I can hear the
grousing already about the need to convert to CP/M. But
console yourself with the fact that I probably would not have
gone to the effort of writing the compiler if I’d been able
to buy one of the already-existing CP/M C compilers.
The I/O routines I chose to support are by no means
the most efficient or universal set, but they run under UNIX,
and as I’ll explain later, there were reasons.
For your own system, there are only a few routines you
will need to support. The runtime library listed here has
considerably more than these, but I use the other routines
only at times when it becomes necessary to step outside the
normal UNIX interface. The routines which the compiler
needs (and which do obey UNIX conventions) are as follows:
1. fopen (sname, mode) char *sname, *mode;
This routine will attempt to open the filename pointed to
by “sname” according to the character pointed to by “mode”.
If “mode” points to an ASCII ‘r’, it will attempt to open for
reading. If it points to an ASCII ‘w’, it will attempt to open
for writing. If the routine can successfully open the file for
the specified mode, it will return a nonzero integer value,
otherwise it will return a zero. The filename obeys the con¬
vention for strings by ending in a null byte (a zero), but other
than that is free to look like a filename specific to the oper¬
ating system. For example, I might attempt “fopen(“<l>
file.tx”, “w”);” where a CP/M user might try “fopen (“B:file.
txt”, “w”);”. On my system, I enforce that no more than one
file be open for output on a given drive at a time. A CP/M
user would probably not need this precaution.
The integer returned by this routine will reflect the “chan¬
nel number” for this particular file. Subsequent reads and
writes will all refer to this number. You may choose to im¬
plement it either as a simple integer (from 1 to N depending
on the number of channels you’ll allow) or an an address of
some form of file control block. UNIX returns a pointer to a
file structure.
2. fclose (iochannel) int iochannel;
This routine will close the file specified by “iochannel”,
which is the channel number returned from fopen(). If that
requires flushing internal system buffers to complete the
file (say, if characters had been buffered in memory instead
of on disk), then this is done. There is no success or failure
indication returned from this routine.
3. getc( iochannel) int iochannel;
This routine will return the next sequential character from
the file specified by “iochannel” (which, once again, is the
channel number returned by the fopen() for this file. If an
error occurs or an end of file is encountered, a — 1 is returned.
A zero character is legal.
4. putc(c,iochannel) char c;int iochannel;
This routine will write the given character “c” to the file
specified by “iochannel”. The character itself is returned if
the write was successful, otherwise a — 1 is returned.
5. gets (buff) char *buff;
This routine inputs characters from the keyboard and
stores them in the buffer pointed to by “buff”. The carriage-
return or newline character terminating the string is replaced
by a null. My version allows simple editing with deletes and
control-X’s, but you can make yours do whatever you like.
6. getchar( )
This routine returns the next available character from the
keyboard. If no character is available, it will wait until there
is.
7. putchar(c) char c;
This routine will print the character “c” onto the user’s
terminal.
The routines given above are probably the minimum num¬
ber you will want to support. They are all the compiler needs,
so for starters, they are probably enough. Adding routines
later is not difficult. In fact, you may have noticed the final
part of the runtime library was written in C to provide a front-
end for some I/O routines I already had. I wrote the necessary
routines compiled them and appended the compiled code to
the library. Total time: maybe 15 minutes.
There are many ways to improve and expand this runtime
library. I already mentioned a few relating to the arithmetic
operators, but I’d like to make a few suggestions about the
I/O routines.
Though many alternatives exist, two which seem immedi-
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Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
ately obvious are (1) make it smaller or (2) make it bigger.
An example of the former was sent to me by Gene Cotton
of Fountain Valley who wanted to put together a minimal
configuration for his system. His approach is straight-forward
and surprisingly lucid. He deleted all my I/O routines, and
added an innocuous routine:
bdos:
CP/M SUPPORT ROUTINE
bdos (DE,C)
char *DE; int C;
returns H=B, L=A per CPM manual
POP
POP
POP
PUSH
PUSH
PUSH
JMP
H
B
D
D
B
H
5
Jiold return address
get bdos function number
get DE register argument
; now put them
back on
the stack
;now off the CPM bdos
As CP/M users can see, this is merely a front end for the
call to location 5 which they have come to know and love.
It takes two arguments which it puts into DE and C respective¬
ly. Hence, a routine to get a character from the keyboard
becomes:
getcharf) (return bdos (1, 1);)
To print a character becomes:
putchar(c) char c; bdos (c, 2); return c; |
In addition to making a tiny runtime library, Gene
further surrounded the code with a “#ASM . .. #ENDASM”
construct (as described in the compiler article), called it “C.
LIB”, and begins his C programs with:
^include C.LIB
This means the runtime library is inserted right into the
file being generated. A nice touch. The only penalty (if you
want to call it that) lies in the need for the user’s program to
do its own bdos() calls to open files, read files, and close files.
If you’re already familiar with the way your own operating
system works and would prefer to continue to work with it,
I would suggest a similar approach. The Code Works (who
are now distributing the little compiler for CP/M) independ¬
ently invented a nearly identical routine to simplify the inter¬
face.
However, if you want to make your I/O libarary independ¬
ent of your operating system, and add some bells and whistles
in the process, I would like to lay out some guidelines for
expansion.
From the very beginning, since C does not inherently pos¬
sess a knowledge of an operating system, people have been
writing their own I/O interfaces to their system. Seeing this as
a serious threat to the portability of the language, the users
eventually came up with a “standard” I/O package.
Rather than reliving this learning experience in the hobby
field, I suggest all implementations and improvements aim to¬
ward this standard. For those who don’t know it, I’ll sum¬
marize the important routines as described in an article called
“A New Input-Output Package” by D. M. Ritchie.
Programs expecting to do I/O usually begin with the line
of code:
#include <stdio.h>
This file contains many vital I/O definitions and para¬
meters. Among them (and worth including in all implementa¬
tions) are:
#define stdin some-unique-value
#define stdout some-unique-value
# define stderr some-unique-value
#define EOF -1
#define NULL 0
#defineBUFSIZ512
These definitions provide system-wide agreement regarding
certain terms, and you will see these in UNIX programs.
The definitions stdin, stdout, and stderr are the first
glimpse of one of the powers of UNIX. They are essentially
default “channel numbers” for the keyboard, the console
screen, and the error device, respectively. They do not need
to be opened with an “fopen( )”, and they can be used in
place of a channel number. Therefore the instruction “getc
(stdin)” would return a single character from the keyboard,
while “putc (c, stdout)” would print the character “c” on the
console. This is not an unusual convention, but the power lies
in the ability of a user at the keyboard to redirect these de¬
fault channel numbers to disk files (or any other peripheral).
Hence, if a program is written to input from stdin and output
to stdout, it will interact with the user terminal in its normal
mode of operation. However, if the user invokes that program
with some syntax like “%foobar > output < input arg arg arg
.. . arg”, he will effectively have opened the file “output”
to receive all writes to stdout, and the file “input” to provide
bytes to reads from stdin. Without modifying the program, it
has been changed to accept input from and send output to
disk files. The channel for stderr cnanot be redirected, how¬
ever, and writing to it will always send the output to the user’s
terminal.
The definitions “NULL” and “EOF” provide names for
some common values (zero and —1, respectively) likely to be
returned by routines. BUFSIZ is merely the size of single
I/O block (a disk sector in practice) and lets the user setup
buffers of the appropriate size if needed. For floppy disk
sytems, BUFSIZ should be defined as 256.
The routines which follow are the most important of the
I/O library. Most are mentioned in the book The C Program¬
ming Language by Brian Kernighand and Dennis Ritchie.
To anyone considering using the C language and especially
those writing their own I/O libraries, I would suggest this
book. For those routines too detailed to discuss here, I will
make references to it.
1. fopen (filename, type) char * filename, *type;
As described above, this routine opens a file for I/O
and returns either a nonzero integer for success or the value
NULL for failure. In addition to ‘r’ for “read” and ‘w’ for
“write”, the argument “type” may point to an ASCII ‘a’
for “append”. My version does not support ‘a’.
2. freopen (Filename, type, iochannel) char *filename,
*type; int iochannel;
This routine closes the file specified by iochannel, and
then reopens it according to the new specifications of file¬
name and type. The value returned is either the new channel
number of NULL.
3. getc (iochannel) int iochannel:
This routine, as described above, returns the next sequen¬
tial byte from the specified file. An EOF is returned for an
end of file or error.
4. fgetc (iochannel).
Just like getc (iochannel).
5. putc (c, iochannel) char c; int iochannel;
This routine, as described above, writes the byte “c”
to the given file. The character is returned if successful, other¬
wise EOF is returned.
6. fputc(c, iochannel).
Just like putc (c, iochannel).
7. fclose (iochannel) int iochannel;
This routine closes the given file. No specific value is
returned.
8. fflush(iochannel)
This routine empties any system-buffered characters to
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 7
315
the file. It guarantees they are transferred to the output
device.
9. exit (errcode) int errocode:
This routine cleans up whatever is needed, and exits
to the operating system, returning the value in “errcode”.
10. feof (iochannel)
This routine returns a nonzero value if the given file
is at the end of file.
11. ferror (iochannel)
This routine returns a nonzero value if an error has oc¬
curred while accessing the given file.
12. getchar()
This routine is effectively “return getc(stdin);”.
13. putchar(c) char c:
This routine is effectively “return putc (c, stdout);”.
14. gets (buffer) char ‘buffer;
This routine inputs a string from stdin. The newline (or
carriage return) character is replaced by a null. It is the user’s
responsiblity to guarantee the buffer is big enough. It re¬
turns either its argument (address of buffer) for success or
NULL for an end of file.
15. fgets (buffer, count, iochannel) char ‘buffer; int count,
iochannel;
This routine reads up to “count” characters into the
given buffer from the specified file. A newline (or carriage
return) character terminates the string and automatically
is followed by a null. It returns either the address of the buffer
for success of NULL if an error occurs.
16. puts (buffer)char ‘buffer;
Writes the null-terminated string from the buffer to
stdout. A newline (or carriage return) is appended.
17. fputs (buffer, iochannel) char ‘buffer; int iochannel;
This routine writes the null-terminated string to the
specified file. No newline is appended. No value is returned.
18. ungetc(c, iochannel) char c; int iochannel;
This routine offends my sense of fair play. It “pushes”
the given character back out the given input file so the next
read will accept it. Only one character may be pushed back.
19. rewind (iochannel) int iochannel;
This routine causes the specified file to be rewound to
the beginning. It is usually used only on input files, since
rewinding an output file essentially discards all previous out¬
put.
20 .
printf(format, al, a2,... an)
fprintf (format, al, a2, ... an)
scanf (format, al, a2, ... an)
fscanf (format, al, a2, ... an)
fread (ptr, size, n, iochannel)
fwrite (ptr, size, n, iochannel)
system (string)
atof (string)
cfree (ptr)
calloc (n, size)
strcat (sl,s2)
strcmp (si, s2)
strcpy (si, s2)
strlen (s)
isalpha (c)
isupper(c)
islower (c)
isdigit (c)
isspace (c)
toupper (c)
tolower (c)
All these are described in the manual. They are all nice to
have but are more suited to a set of utility programs (maybe
kept in a separate file) than they are to a runtime library.
There are a few other routines not mentioned, but not all
of them are supported even on UNIX systems, so they have
been omitted. Not all of the routines above need to be sup¬
ported, but at least you have an idea of what a full implemen¬
tation would entail
As I mentioned, my version supports only the minimum
number of these routines, and it does not know about stdin,
stdout, or stderr. Actually, the version I am currently working
on in my spare time will be very close to everything I have
described above. As I mentioned before, it will contain Charles
Falconer’s floating point routines.
To make C programs run in an environment more similar
to UNIX, I am making the compiler (via the routine header
()) begin all programs by generating a call to a routine named
“enter” which will do all necessary system housekeeping,
will pull arguments off my system command line into a con¬
struct like the ARGV, ARGC from UNIX (which I won’t
describe here, but which is described in detail in the manual)
and will call “main ( )”. When “main ()” returns, it will
return control to the routine “exit” which will close all files
left open before returning to my operating system.
In time, I may not even return to the operating system.
Consider a small UNIX-style shell (command line interpreter)
which takes the place of the operating system (but which uses
all the hooks available). With a powerful I/O library and the
ablity to redirect stdin and stdout, it seems obvious that the
notion of a micro-UNIX is not far fetched.
Interested? Well, at the moment, you have all the tools
available that I do: (1) A compiler, (2) a standard I/O library,
and (3) an already existing operating system to use as an
example. For starters, that ain’t half bad.
LISTING
;••••••«..............
1
; Runtiae Library tor Saall C Ccspiler
;
? by Ron Cain
i
}
;
>
;Petch a single byte froa the address in HL and
i sign extend into HL
ccgchar: MOV A/M
;Put the accua into HL anc sign extena through H•
CCSXt: MOV L/A
RLC
SBB A
MOV H/A
RET
;Petch a full 16-bit integer froa the address in HL
;lnto HL
ccglnt: MOV A,M
INX H
MOV U/M
MOV L/A
RET
jStore a single
ccpchar: MOV
STAX
RET
;Store a 16-bit
ccplnt: MOV
STAX
IMX
MOV
STAX
RET
;Inclusive "or"
ccor: MOV
ORA
MOV
MOV
ORA
MOV
RET
byte froa HL at the address in 0E
A/L
0
integer in HL at the address in CE
A/L
0
0
D
HL and DE into HL
A/L
E
L/A
D
H/A
;Excluslve "or**
ccxor: MOV
XRA
MOV
MOV
XRA
MOV
RET
HL and DE into HL
A/L
E
L/A
A/H
D
H/A
;"And" HL and DE into HL
ccand: MOV A/L
ANA E
MOV L/A
Page 8
316
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
11 the lollowlng coapare routines/ HL Is set to 1 12 the
ltlon la true/ otherwise it is set to 0 (zero).
if HL « DE
CALL cccap
RZ
DCX H
RET
If DE 1= HL
CALL cccap
RNZ
DCX H
RET
If DE > HL (signed)
XCHC
CALL cccap
RC
DCX H
RET
If DE <=* HL (signed)
CALL cccap
RZ
RC
DCX H
RET
If DE >= HL (signed)
CALL cccap
RNC
DCX H
RET
If DE < HL (signed)
CALL cccap
RC
OCX H
RET
; of DE and BL
>Thls routine pertoras DE - HL and sets the conditions:
) Carry reflects sign of difference (set aeans DE < HL)
) Zero/non-zero set according to equality.
;Subtract HL froa DE and return In HL
ccsub: MOV A,E
SUB L
NOV L/A
MOV A/D
SBB H
MOV H,A
RET
>Pora the tuo's coapleaent of HL
ccneg: CALL cccoa
INX H
RET
)Pora the one's coapleaent of HL
cccoa: MOV A,H
CMA
MOV H,A
MOV A,L
CMA
MOV L/A
RET
;Multlply DE by HL and return in HL
H
ccault: MOV
E/H
MOV
C/L
HL (signed)
LXI
h/C
cccap
ccaultl: MOV
A/C
RRC
JNC
cciult2
H
CAC
C
ccault2: XRA
A
HL (signed)
MOV
A/B
cccap
RAR
MOV
B/A
H
MOV
A/C
RAR
iL (signed)
MOV
C/A
cccap
CRA
B
RZ
H
XRA
A
MOV
A/E
RA
i to perfora a signed coapare
MOV
E/A
MOV
A,D
*mmA
MOV
A/B
SUB
L
MOV
E/A
MOV
A/D
SBB
H
LXI
H/l
/preset true
condition
JM
cccapl
ORA
E
2 "OR" resets
carry
RET
ORA
E
STC
;set carry to
signal alnus
RET
;Test If DE >- HL (unsigned)
ccuge: CALL ccucap
RNC
DCX H
RET
;
;Test If DE < HL (unsigned)
ccult: CALL ccucap
RC
DCX H
RET
;
;Test if DE > HL (unsigned)
ccugt: XCHC
CALL ccucap
RC
DCX H
RET
;
;Test if DE <= HL (unsigned)
ccule: CALL ccucap
RZ
RC
DCX K
RET
;
;Coaaon routine to perfore unsigned cocpare
;carry set 11 DE < HL
;zero/nonzero set accordingly
ccrdel
ccclv2
cccapbcde
ccdlv2
A/L
1
L/A
A/E
C
E/A
A/D
ccucap: MOV
CMP
JNZ
MOV
CMP
ccucapl: LX1
RET
A/0
E
ccucapl
A/E
L
h/1
;Shlft DE arithaetlcally right by HL and return in HL
ccasr: XCHG
MOV A/H
MOV L/A
OCR E
JNZ ccasrei
RET
;Shift DE arithaetlcally left by HL ana return In HL
ccasl: XCHG
DAD H
DCR E
JNZ ccaslel
RET
;Divlde CE by bL and return quotient in HL/ reaalnder In CE
;(slgned divide)
ccdlv: MOV E/H
NOV C,L
MOV A/0
XRA fa
PUSH PSfa
MOV A/D
ORA A
CM ccdeneg
MOV A/B
CRA A
CM ccbcneg
MVI A/16
PUSH PSfa
XCHG
LXI C/C
ccdivl: DAD H
CALL ccrdel
JZ ccolv2
CALL cccapbcde
JM ccdiv2
MOV A/L
OR 1 1
MOV L/A
MOV A/E
SUB C
MOV E/A
MOV A/D
SBB B
MOV D/A
ccdlv2: POP PS fa
DCR A
JZ ccdlv3
PUSH PSfa
JMP ccdivl
ccdlv3: POP PSfa
RP
CALL ccdeneq
XCHG
CALL ccdeneg
XCHG
RET
;Negate the Integer in DE
;(internal routine)
ccdeneg: MOV A/C
CMA
MOV D/A
MOV A/E
CMA
MOV E/A
INX D
RET
;Negate the integer in PC
;(internal routine)
ccbcneg: MOV A/B
CMA
MOV fa/A
MOV A/C
CMA
MOV C/A
INX B
RET
>Rotate DE left one bit
)(internal routine)
ccrdel: MOV A/E
RAL
MOV E/A
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 9
317
MOV
A/C
RAL
MOV
D/A
ORA
E
RET
/Coapare BC to
DE
/(internal routine)
cccapbcde: MGV
A/E
SUB
C
MOV
A/D
SBB
E
RET
/
;I/0 subroutines
;
;lnput a character into HL
getchar: CALL *H0 ;Get one
JMP ccsxt /Sign extend
;
/Output a character (putchar(char))
putchar: LXI h/2
DAD SP /index past return
POV A/P ;get char
CALL AH1
JMP ccsxt
/
;Test for a character(return in HL if tound/but con't dequeue)
CHRDY: LHLO KB1G
LDA KBIP
SUB L
JZ chrhyi
PGV A,P
CHRDYl: JPP ccsxt
?
;Disle file I/O
;
FDENUP EQU 4 /Number files supportec at once
FDESIZE tQU 310 /Number tytes required tor each file
)
/Offsets into unit tables
FDISKADD EQU 45
FSECTCNT EQU 4?
FBYTEOFF F.QU 49
FBUFF EQU 50
;
;Open a tile
;Call: F OPFN(oirection/un it/size/naaeptr)
; direction = 1 to read/ 2 to urite
; unit = 1/ i, 3/ ...(# units avail)
; size = iax size (ignored)
; naseptr = addr of asciz filenaae
;Returns: 0=good opwi/ -l = open failure
;
FOPEN: LX l h/2
LAD SP ;ptr to arg list
LX 1 C/FOPARGS
PVI C/8
FOP1: POV A,P
STAX C
1 NX h
1 NX C
OCR C
JNZ F0P1 /transfer args to usable area
CALL FOPFDE ;gtt unit's tlock
JC FOPERR
MOV A/M ; icle?
GRA A
JNZ FOPERR
XR A A
STA NFL IR /force directory load
LHLD FILERAMF
XCHG
LXI H/FF1LE
M VI C/CFFH
FOPENl: LDAX C /Get fllenate
MOV P/A
INX h
I NX D
IN R C
GRA A
JNZ
FOPENl
MOV
A/C
ORA
A
JZ
FOPERR
/Null
DCX
H
MV1
M/ODH
/append <CR>
LHLD
FDE
INX
H
XCHG
/DE = FDE addr
LXI
H/FFILE
LXI
B/ *T X '
MV I
A/ 60 H
CALL
Qvrto
DB
•Gfid*
PUSH
PSb
LDA
PTYPE
DCR
A
JNZ FOPNRITE
LXI B/FDESIZfc
MV I A/(FUENUM AND OFFH)
FOPNRTl: PUSH PSh
POV A/P
CPI 2
JNZ FOPWRT2
INX H
MOV A/P
DCX H
ANI 3
CMP D /any other writes on this drive?
JNZ
PQPNRT2
INN
E
FOPWRT2: DAD
B
POP
PSh
DCR
A
JNZ
FOPNRT1
MOV
A/E
ORA
A
JNZ
/File looks ok
FOPERR /yes...fail
FQPOK: LHLD
FDE
INX
H
INX
h
POV
A/P
1NR
A
INR
A
1NR
A
ANI
01FH
MOV
C/A
MVI
B/0
DAD
E
XCHG
;Ct = 0FDA
LHLD
FDE
LXI
B/FDISKADD
DAD
B
MVI
C/4
FOPOKl: LDAX
D
MOV
M/A /copy FDA A DN!
INX
H
INX
C
DCR
C
JNZ
FOPOKl
XR A
A
POV
P/A /clear byte of:
FOPQK2: INX
H
PVI
P/0
LCR
A
JNZ
FOPOK2 /clear butter
LHLD
FDE
LXI
B/FDISK ADC
DAD
B
MOV
E/P
INX
H
MOV
XCHG
D/P
LXI
0/350
MOV
A/H
CMP
D
JNZ
F0P0K3
MOV
A/L
CMP
E
POPOK3: JNC
FOPERR /At end of dls!
LHLD
FDE
LDA
FTVPE
MOV
M/A /declare open
LXI
RET
H,C
FOPERR: LXI
RET
H/-I /open error
/
/Find the unit
block for unit in FUNIT
/carry set on
error
FOPFDE: LDA
FUNIT
MVI
8/(FDENDM AND OFFH)
LXI
C/PDESIZE
LXI
H/FDEBUFF
FOPFDE1: DCR
A
JZ
FOPFDE2
0 AD
C
DCR
B
JNZ
FOPFDE1
STC
RET
/error
FOPFDE2: SHLD FDE
STC
CMC
RET
;
/Close a file
/Call: FCLGSE(unit)
/no returned value
rCLOSE: LXI H/2
DAD SP
MOV A/M /get unit
STA FUNIT
CALL FOPFDE
RC
Page 10
318
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
CALL
JNC
* LXI
DAO
MOV
IN X
MOV
DCX
MOV
ORA
STC
CMC
RZ
PUSH
LHLD
INX
INX
MOV
INR
INR
INR
ANI
MOV
M V1
CAD
INX
INX
POP
MOV
INX
MOV
LHLC
INX
MVI
CALL
DB
RET
froir a
FHRTB ;eapty systen buffer
FCLSUT
LHLD FDE
B/FSECTCNT
B
E/M
H
C/M
fa
*/E
C
C
FDE
H
H
A/M
A
A
A
01FH
C/A
b/0
B
fa
fa
c
M/E
fa
P/C
FDE
H
A/1
Cvrto
'Gfid'
;nothing written
;dns
;put in FDE
jRead
;caii: freadob
; .oenaadr
; fcytes =
/Returns: -1 =
; else
/
FREAD:
/Main
PREAD1
(ie C =
CALL
LXI
SHLD
CALL
JC
MOV
OCR
JNZ
read lcop
LHLC
MOV
CRA
JZ
MOV
ORA
JNZ
;less than 256
;Mor e
FREAD3
file
emaodt/oyteS/unit) \
= beginning addr of user butter
positive nunter cf bytes to read
error in read
returns nuater of bytes successful
end of file)
FDE
B/FDISKADC
B
A/E
M
M/A
H
A,C
M/A
H
A,M
E
M/A
H
A/M
C
M/A
FMEM
B/E
C,C
B
FMEM
FXFER
e
FXFER
A,B
e,»
a,c jSmwK.
;tunp ahead disk addr
;count off # sectors
/Bake n bytes
;tump ahead net addr
V bytes read
i-t?
FCNT '/
FCNT /count down A bytes
FREAD1 ;loop
;Read a single byte into user's aenory
)carry set if error
F X ARCS
h /0
FXFER
FOPFuE
FXFERR
A/M
A
FXFERR
FCNT
A/H
L
FXCK
A/h
A
FREAD3
■ / l-C-.. v
FREADB: LHLD
LXI
DAD
MOV
ORA
JNZ
FDE
B/FBYTEOFF
B
A/M
A
FHCBYT
;nothing in system buffer
;preset xter cnt
; done
CALL
FREADP
;read a byte
JC
FXFERR
JMP
FREAD1
;ar.d loop till done
than 256
leans we
go direct to user nevory
1: LHLD
FDE
LXI
B/FBYTtOFF
DAD
B
MOV
A/M
CRA
A
JZ
FREAC5
CALL
FREADB
;ye have some in systes cuff first
JC
FXFERR
JMP
FR EADI
LHLD
FDE
LXI
B/FSECTCNT
DAD
B
MQV
E/M
INX
1!
MOV
C/M
;0E = g sectors left
LOA
F CNT *1
;get »sb A bytes
MVI
h/0
;HL = A sectors requesteo
MOV
A/h
CMP
D
JNZ
FREAD6
MOV
A/L
CMP
E
>: JC
FREAD7
XCHG
;user wants too nany
MOV
A,H
CRA
L
JZ
FXQK
;if zero*..done
PUSH
H
;save A to read
MOV
A/L
/(A < 256)
PUSH
PSh
LHLD
FDE
INX
H
MOV
A/M
ANI
3
MUV
C/A
;unit
MVI
B/l
;read end
LXI
D/FD1SKADD-1
CAD
D
MOV
E/M
INX
H
MOV
D/M
;CE = disk addr
LHLD
XCHG
FMEM
/HL = mem addr
POP
FSb
CALL
Dio
; read
POP
B
/A attempted
JC
read
FXFERR
XCHG
;DE = # sectors read
CO
s
Dr. Dobb's Journal of Computer Calisthenics
DCX
H
MOV
A/M
DCX
H
ORA
M
/ an;
JZ
FRDBX
; no
DCX
fa
MOV
C/M
DCX
fa
MQV
E/M
;DE
PUSH
C
LHLD
FDE
INX
fa
MOV
A/M
ANI
3
MOV
C/A
;un
MVI
B/l
; r e
LXI
C/FRUFF
-1
DAD
XCHG
C
/ in
PUP
h
MVI
A/l
; i
CALL
Cio
RC
;er
LHLC
FDE
LXI
B/FD iSKADC
DAD
E
INR
M
INX
h
JNZ
FPCB<
INR
F
;bu
INX
H
MOV
A/M
ORA
A
JNZ
FRC9 J
CCR
M
;ce
INX
fa
DCR
M
XRA
A
;buirp disk addr
cecrement sector court
;accufl< = offset to next byte
FDE
B/FBLFF
LHLC
LXI
DAD
MOV
MVI
DAD
MOV
LHLD
MOV
INX
SHLC
LHLD
INX
SHLD
LHLD
DCX
SHLD
LHLD
LXI
DAD
INR
STC
CMC
RET
C/A
B/0
B
A/M
FMEM
M/A
H
FMEM
FXFF.K
fa
FXFER
FCNT
h
FCnT
FDE
B/FBVTEPFF
B
;get byte
;put in user memory
;fcunp offset (C aeans empty)
;Read/w
rite okay
FXOK:
LHLD FXFER
;get A bytes
REI
FXFERR:
LXI C/-1
;ecror exit
RET
;
/Transfer the
arguments
from the stack
FXARCS: LXI
H/4
DAD
SP
LXI
D/FXALIST
MVI
C/6
FIALP: MOV
X/N
STAX
D
INX
H
INX
C
DCR
C
JNZ
FX ALP
RET
;
;
;Mrlte to a rile
/Call: FnRITE( memadar/l
tytes/unit) , .
; (see FREAD
;
for explanation. ..they are same)
ransfiff
FNHITl: CALL
FXARGS
LXI
SHLD
H/0
FXFEP
CALL
foppnr
JC
FtfFEFP
NOV
A/N
CPI
2
JNZ
F XFFRR
/Main writing
loop
.V jf»». .
FMRITEl:
LHLD
'«« i? WP
MOV
A/H
CRA
L
JZ
FXGK
/cone
MOV
A/H
ORA
A
JNZ
FNRITE3
/less than 25
6
FNRITE2:
CALL
FNRTB /write a byte
JC
FXPERP
JMP
FWRITE1
/more than 25
6 means it
goes direct to user
FMRITE 3:
LHLD
FDE
LXI
B/PBYTEOFF
CAD
e
NOV
A/M
JNZ
FWRITE2
/empty internal buffer first
LHLD
FDE
LXI
B/FDISKAOD
DAD
d
NOV
E/M
INX
H
MOV
D/M
MOV
A/E
CMA
MOV
E/X
MOV
X/C
CMA
MOV
D/X
INX
D
/-FDA
LXI
Hz 349
DAD
XCHG
C
/349-PDA = X sectors till end
LDA
FCNTM
MOV
L/X
MVI
H/0
/make HL = # requested
MOV
A/H
CMP
D
JNZ
fWRITE4
MOV
X/L
CMP
E
FMRITE4:
JC
FNFITE5
XCHG
/can't do this many
FWRITE5:
MOV
A/H
ORA
L
JZ
FXUK
/no room at all
PUSH
H
MOV
X/L
PUSH
PSN
LHLD
FDE
INX
H
MOV
X/M
ANI
3
MOV
C/X
/unit
MVI
B/0
/write cmd
LXI
C/FD ISK ADC-1
DAD
MOV
D
E/M
rar
INX
MOV
H
0/M
LHLD
FNEM
XCHG
POP
CALL
POP
JC
PSm
Clo
C
FXFERP
/good write
LHLD
FDE
LXI
B/FD ISKADD
DAD
B
MOV
A/E
ADD
M
MOV
M/A
INX
H
MOV
A/D
ADC
M
MOV
P/X
INX
H
MOV
X/E
AUD
M
MOV
N/X
INX
H
MOV
X/C
ADC
M
MOV
N/X
LHLD
FNEM
MOV
B/E
MVI
C/0
/make fi bytes
DAD
6
SHLC F HfcM
LHLC FXFF.R
CAC B
SHLD FXFER
► Q V A/t
C W A
►UV B/A
nuv A/ c
CMA
MOV C/A
1 NX H
LHLO FCNT
CAB e
SHLD FCNT
LHLC FDt
LX I B/FDISKACO
BAD b
HCV £,#-
1 NX h
NOV C/M
X CHC
LX1 C/JSC
NOV A/H
CNP L
JNZ FNRITF6
NOV A/L
CMP fc
PNRITEto: JC FNRITE1 /still room on disk
BMP PICK ;cisk full/ but no more/ please
;
/Write a single byte from user memory
;carry set it error
FWRTB: LHLD FOE
LX1 E/FBYTECFP
CAD B
PUSH H
MOV C/M
I NX h
MVI B/0
DAD B ;lndex to place to put it
XCHG
LHLD F MEM
MOV A,N
STAX D /copy to system buffer
IN X H
SHLD FNEM
LHLD FXFE(<
1NX H
SHLD PIFER
LHLD FCNT
OCX H
SHLD FCNT
POP H
1 NR M ;bump oflset
JZ FNRTBl ;opps/ filled buffer
PWRTBX: STC
CMC
RET
;Need to write system butter to oisk
FNRTBl: 1 NX H
PUSH H ;Rbuff
LHLC FOE
1 NX h
MOV A/M
ANI 3
MOV C/A ;unlt
MVI B,0 ;write c«a
LX1 D/FD1SKADC-1
0 AO 0
MOV A,N
INX H
MOV H/M
MOV L/A /get the disk addr
POP D ;DE = mem addr/ HL = disk addr
MVI A/1
CALL Dio
RC ;error
LHLC FOE
LX 1 B/FD1SKAU0
DAO B
I NR M ;bump ND A
INX H
JNZ FMRTE3
INF N
FNRTB3: INX H
INR M /A TINS
INX h
JNZ FNRTB4
INR M
FWRTB4: INX H
INX H ;HL = § buff
XRA A
FNRTB5: MVI M/C
INX H
INR A
JNZ FMRTR5 ;clear buffer after every write
LHLD FDE
LX I B/FDISKADC
0 AD B
NOV E/M
INX h
NOV D/M
XCHG
LXI C/350
Mil V A/H
CMP C
JNZ *«RTfc6
NOV A/L
CMP t
FNRTB6: JC FMRTcX ;still room
LXI H/C
SHLD FCNT /tull...ro more can be done
LHLC FDE
LXI B/FBYTLOFF
DAD B
h vI M/C ;and declare butter empty
Page 12
320
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
?File I/C storage area
;Followlng are the argurents
PQPARGS:
FILENAME: DS 2
FNUHd: OS 2
fxalist:
FUNIT: OS 2
FCNT:
FTYPE: DS 2
FHEN*. os 2
jStart ol local storage
FDE: DS 2
FXFERS DS 2
ffile: ds 40
fzero: OS 1
;
;Unit block foraats:
; *0 = type of op
; *1 = Poly FDE b
; *45 = FDA (also
; »47 = DNS sector
; +49 = offset to
; ♦50 = internal b
fdebuff: cs
;Addr file nane
;Size on open (unused)
direction of transfer
;Current rerory address
;Acdr of current unit block
;ft bytes done
;fllenaae buffer
;known null wcrd tor closing
type of open (0 = tree/ 1 = reac, 2 = write)
Poly FDE block (aax 44 bytes)
FDA (also NDA) next disk addr fcr xfer
DNS sector count (reads decreaerts/ write inc's)
offset to next byte in Internal fcuifer
internal buffer (256 bytes)
CS FEESIZE • FDENUN
DS 10 ;tudge factor
)
/Following are scae routires written in C to provide a UNIX coapatible
/front-eno tor the already existing I/O routines.
;
;saall-c coapiler rev 1.0
;/• •/
;/* Patch to poly I/U routines •/
;/• */
;fdeflne NULL 0
;fdefine eol 13
;fopen(snaae/aode)
fopen:
y-.-V
v:?'
char *snaae/*aode;
int xferaoae/unit;
PUSH b
PUSH B
11(*iodi*='v')xferaode=2;
LXI H/6
DAD SP
CALL ccgint
CALL ccgchar
PUSH H
LXI H/115
POP D
CALL cceg
MOV A/h
ORA L
JZ CClOOOl
LXI H,2
DAD SP
PUSH H
LXI H/2
POP C
CALL ccpint
else xferacde=l;
JMP cc10002
LXI h/2
DAD SP
PUSH H
LXI H/l
POP D
CALL ccpint
unit=0;
LXI h,D
DAD SP
PUSH H
LXI H/0
POP 0
CALL ccpint
while(unit<4)
LXI h/0
DAD SP
CALL ccgint
PUSH H
LXI H/4
POP C
CALL celt
NOV A,H
ORA L
JZ ccl0004 . v
if (FLFtN(xferaode/^urit/-l/snaiie) = = 0)
LXi H/2
DAD SP
CALL ccgint
PUSH H
LXI H/2
DAD SP
PUSH H
CALL ccgint
1 NX h
POP C
CALL ccpint
PUSH H
LXI H/l
CALL ccneg
PUSH H
LXI h/14
DAD SP
CALL ccgint
PUSH H
CALL FOPEN
XCHG
LXI H/o
DAO SP
SPHL
XCHG
PUSH H
LXI H/0
POP C
CALL cceq
MOV A,H
OR A L
JZ CC10005
; return unit;
LXI H/0
DAD SP
CALL ccgint
POP B
POP B
RET
; return NULL;
CC10005:
jmp ccioooa
cciooo4:
LXI H,0
POP B
POP B
RET
; >
;fclose(unit)
fclose:
; int unit;
>C return FCLOSE(unit);
LXI H/2
DAD SP
CALL ccgint
PUSH H
CALL FCLCSE
POP B
RET
>>
;getc(unit)
gate:
; int unit;
;( char buttCll/int flag;
OCX SP
PUSH B
; tlag=FREAD(buff/l/unit);
LXI h,0
DAD SP
PUSH H
LXI H,4
DAD SP
PUSH H
LXI H,1
PUSH H
LXI H,11
DAD SP
CALL ccgint
PUSH H
CALL FREAD
POP B
POP B
POP b
POP C
CALL ccpint
; 11 ((tlag = = C)|(tlag = =-l))return -1;
LXI H/0
DAD SP
CALL ccgint
PUSh H
LXI H/0
POP c
CALL cceq
PUSH H
LAI H,2
DAD SP
CALL ccgint
PUSh H
LXI H/l
CALL ccneg
PLP C
CALL cceq
POP D
CALL ccor
MOV A/H
ORA L
JZ ccl0006
LXI H/l
CALL ccneg
I NX SP
POP B
RET
; return(buffC0]L255);
cclOOOb:
LXI H/2
DAD SP
PUSH H
LXI H/0
PUP C
DAO 0
CALL ccgchar
PUSH H
LXI H/255
POP C
CALL ccand
I NX SP
PUP B
RET
; )
;putc(c/unit)
putc:
; char c;int unit;
;( char buffC13;int flag;
DCX SP
PUSH B
; buffC03=c;
LXI b/2
DAD SP
PUSH H
LXI H,0
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 13
321
PGP D
DAO C
PUSH H
LXI h/9
LAD SP
CALL ccgchar
POP D
CALL ccpchar
flag=P»RITE(buff/1/unit);
LXI h/Q
CAD SP
PUSH H
LXI H/4
DAD SP
PUSH H
LXI H/1
PUSH H
LXI H/ 11
DAD SP
CALL ccgint
PUSH H
CALL FtaRITE
PGP c
POP E
PUP E
PGP C
CALL ccplnt
if((flag==C)l(flag==-l>>return
LXI H/0
DAD SP
CALL ccgint
PUSH H
uXl h/0
PGP C
CALL cceg
PUSH H
LXI h t i.
DAD SP
CALL ccgint
PUSH K
LXI h/1
CALL ccneg
POP D
CALL cceq
PGP C
CALL ccor
MOV A/H
CRA L
JZ ccl0007
LXI h/1
CALL ccneg
IN X SP
POP fc
RET
else return(c&255);
jmp ccioooe
LXI h/7
LAD SP
CALL ccgchar
PUSH H
LXI H/^5S
POP L
CALL ccand
I NX SP
POP k
PET
>
cclOOOB:
;
1 NX SP
POP h
hET
;gets(butt )
gets:
chat buttC);
PUSH H
LXI h/24
POP C
CALL cceg
NOW A/H
CRA L
JZ cclOOll
LXI H/0
DAD SP
PUSH H
LXI H,0
POP C
CALL ccpint
LXI h,24
PUSH H
CALL putchar
POP B
else
JMP ccl0012
LXI H/4
DAD SP
CALL ccgint
PUSH H
LXI H/ /.
DAD SP
CALL ccgint
FOP C
CAD C
CALL ccgchar
PUSH K
LXI b,121
POP C
CALL cceg
NOW A/H
OKA L
JZ ccl0013
LXI E/0
DAD SP
CALL ccgint
PUSH H
LXI H,0
PUP L
CALL ccgt
MOV A/H
Ch A L
JZ ccl0014
LXI P/O
DAD SP
PUSH H
LXI H/ 2
DAD SP
CALL ccgint
PUSH F
LXI H,1
FOP C
CALL ccsth
PGP C
CALL ccgint
LXI H,127
PUSH H
CALL putchar
PGP b
cclOOlA:
mm
cclOOl3:
;
else
JMP cclOC15
int <;
PUSH 3
* = 0 ;
LXI r/0
CAD SP
PUSH H
LXI h,0
POP C
CALL ccpint
while((biflCPl=getchar())!=eol)
LXI h/4
LAC SP
CALL ccgint
PUSH H
LXI h/ 2
CAD SP
CALL ccgint
POP C
DAD D
PUSh H
CALL getchar
POP C
CALL ccpchar
PUSh H
LXI H/13
FOP C
CALL ccne
MOV A/b
ORA L
JZ ccl0010
(
it(buffCk3--24)(k-0;putchar(24);)
LXI h/4
DAD SP
CALL ccgint
PUSH H
LXI b/2
DAD SP
CALL ccgint
POP C
DAD C
CALL ccgchar
LXI H/4
CAD SP
CALL ccgint
PUSH H
LXI H/2
0 AD SP
CALL ccgint
FOP C
CAD C
CALL ccgchar
PUSH H
CALL putchar
POP B
LXI h/U
CAD SP
PUSH H
LXI H/2
DAD SP
CALL ccgint
PUSH H
LXI h,l
POP C
CAD C
PGP C
CALL ccpint
cc10015:
ccl0012:
JPF ccICC09
buffCkJ=C;
LXI H/4
DAC SP
CALL ccgint
PUSh H
LXI H/2
CAD SP
CALL ccgint
PUP C
DAD 0
POSH H
LXI h/0
POP C
if(buffCkJ==127)
( iX(k >0 )
(K=k-1;
putchar(127);
)
)
(
putchar(tut fck 1);
k = k*l;
Page 14
322
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
CALL ccpchar
putchar(eol);
LXI h/13
PUSH H
CALL putchar
POP E
return buff;
LXI H/4
DAD SP
CALL ccgint
POP E
PET
;0 errors in compilation.
; >>>>> end of run
&
.vr-. AH-; A
>>>>> er.d of runtime library <<<«
ENDING
F
fi.tigi
fi£.
•svi' .J rs-C/‘. if5^i
Wif^j4>V%4
®8SSI@
Jffel
ar
rawsftir
mm*
M.
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 15
323
^ Thoughts on Small Systems and Monitors
(mostly the SYM-l)
BY H. T. GORDON
College of Natural Resources
University of California
Berkeley CA 94720
I define a “small” system as one that is
owned and used by only one person.
This still allows more than a ten-fold
range in cost and complexity, but the
common ground is the man/machine
interaction that can be (for the human
being) a profound educational experience.
My first system was a KIM-1, the crea¬
tion of Don McLaughlin while he was at
MOS Technology. This early SBC launch¬
ed the new 6502 (in the dim and distant
past of 1976!) and, together with bril¬
liant descriptive manuals, played a major
role in its popularization. It was—belat¬
edly— emulated by the makers of other
microprocessors, and of course surpassed
by more complex systems of the multi-
board type. As a learning tool it still has
few (perhaps no) equals. All of my
previous communications, in DDJ and
elsewhere, were worked out on my KIM.
One of its invaluable assets is the com¬
plete and quite well-commented listing of
the code of its 2K ROM monitor, a
simple “operating system”, rich in
information on how to program. Like
other users I soon became aware that
many of its routines were callable by
new programs, although this had not been
clearly foreseen by whoever wrote the
monitor programs. By now, this ought
to be recognized as one of the major
functions of every monitor: to provide
a “library” of efficiently-coded routines
accessible to newly-created main pro¬
grams. In a ROM, the need to squeeze
many operations into a limited space
will often cause brevity of code to be
given priority over maximum speed of
execution. Also, subprograms will tend to
be special-purpose instead of general-
purpose. You can’t have everything!
However, one service that ought to
be included with the documentation of a
monitor listing is a list of user-accessible
subroutines, so that users need not waste
time searching them out. Such a list may
be longer than the number of RTS in¬
structions in the monitor, since a sub¬
routine may have several useful entry
points (including some undreamed of
by the person who wrote it!) The use of
more than one exit point, which can
sometimes enhance both code efficiency
and timing, is often stigmatized as “un¬
structured.” That’s a word I have come to
dislike. Everything has structure. The
distinction that matters is intelligibility ,
and this is not necessarily lost by using
two (or even more) exit points. What
must be avoided is excess of any kind,
including excessive rigidity and com¬
plexity.
The Upgrading/Customization Prob¬
lem. Everyone must sooner or later out¬
grow a system as confining as an SBC,
and the question becomes: upgrade to
what? More crucial still, for what?
Perusing the articles and ads in micro¬
computer journals is bewildering. So
many competing systems, add-on peri¬
pherals, interfaces, languages, complex
softwares, and above all uses! I long
deferred any upgrading decision, in the
hope that major innovations would soon
appear. My concept of my own needs
gradually crystallized: a system that
could sense, measure, analyze, and act on
the outside in a way similar-but super¬
ior-to the way I do and so do my work
for me.
While “dedicated” microprocessors are
already automating a variety of instru¬
ments, that’s not quite what I want.
There’s a colossal wastage built in to the
scientific (and doubtless also the busi¬
ness) world, caused by non-standardiza¬
tion, deliberate avoidance of modularity/
interchangeability, and planned obsoles¬
cence.
Except at the leading edge, where
state-of-the-art can only be had by
custom design, “packaged” systems domi¬
nate scientific laboratories. Each has its
built-in electronics, recorders, etc., so
tied together that if one element obso-
lesces, the whole thing must be thrown
away, brushed-aluminum chassis and all.
These genies simultaneously serve and
enslave their users, who become button-
pushers with no comprehension of or
power to modify the mechanisms.
The concept that has always appealed
to me is more that of the “hi-fi” enthu¬
siasts, where a system consists of several
interacting but independently-replaceable
components, from many competing
sources. True competition, however ab¬
horrent to industrial giants, makes pos¬
sible a maximum of progressive change
at the minimum cost to society. This
eccentric, unbundled-components point
of view enabled me to resist the lure of
the increasingly powerful packaged sys¬
tems that have entered the market in
recent years. However flexible, they must
be designed for some least-common-de-
nominator purpose and tend to allocate
large resources to things like BASIC
interpreters (for me a turn-off). They
are like low-cost smoothly-paved roads
leading to where everyone else wants to
go.
My first upgrade was a Synertek SYM-
1. It is even more flexible and I/O-
oriented than the KIM. Even future-
oriented, since major ICs are socketed
and one hopes that upgrading from the
6502 to the 6516 will be easy. The SYM
is a masterwork, complex and not free
from flaws, that encourages and even
compels its user to explore unbeaten
paths. It works best only for someone
willing to make the effort to under-
Page 16
324
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
stand it.
One thing the SYM can do is inter¬
face with a TTY or CRT terminal, via
RS-232 at baud rates from 110 to 4800
(well below the potential of a 6502
CPU). It is obvious that a CRT—not a
TTY—is the primary upgrading element
of an expanded system. The Commodore
PET built one in, while the Apple II,
TRS-80, etc., built in only an ASCII
keyboard and allow (really require)
interfacing to a TV monitor. These sys¬
tems tend to have less than the 24 x 80
character display of stand-alone CRT
terminals, but to some extent compen¬
sate this by providing graphics, and
sometimes color. Many of their limita¬
tions will soon be transcended (probably
first by the Apple III). Conventional CRT
terminals will soon face superior price/
performance competition, and their too-
high price is already falling. I therefore
decided to buy one, the Televideo 920-B,
that seemed a fair value at its current
near-$800 mail-order price. It lacks the
graphics capability of the 920-C, but
I don’t mind that since my mind is a
symbol-oriented algebraic, not a geo¬
metric one. Of course, so-called “printer
graphics” of the TTY type are possible.
The 920-B is an “intelligent” terminal
controlled by an Intel 8035 micro-pro¬
cessor, with a 32K ROM and sockets
for 8 high-speed 2114 static RAMs
(allowing storage of an “alternate” 24 x
80 character page). Competitive pressure
has now made all intelligent terminals
so good that I have no idea whether the
920-B is one of the “best,” but it is
very satisfactory. I like its eleven “func¬
tion” keys, that send a 3-character mes¬
sage to the computer: 01-XX-OD, where
XX ranges from 40 to 4A with the F
keys alone, and from 60 to 6A if the shift
key is also depressed, for a total of 22
different commands. The user decides
how the computer shall interpret them.
It also has its own RS-232 interface to
a printer, so that the user can print ex¬
actly what he sees on the screen.
When I connected the 920-B to the
SYM-1, the log-in command (S, J, 1,
CR) from the STM’s onboard keyboard
did not work. A study of the monitor
listing led me to modify the vector in the
monitor RAM at $A622 from its set
value of $A7 to $71. This worked, prov¬
ing that having a listing—and being able
to read it —is a good thing, and also that
the redundancy of dual control has
merit.
The slowness of 4800-baud serial
transmission (that seems to fill the screen
at about 80 characters/second) is a shade
annoying to a lover of speed. The 920-B
can work at 9600 baud (very good
for serial), but the SYM designers were
not thinking in those terms. Although
I’ve known the theory of communication
from books, this first real-life encounter
with it has been educational. One sym¬
pathizes with the problems ot the
pioneers trying to drive messages through
long transmission lines—losses, noise,
errors and the like—and sees the why of
parity and checksums. The SYM monitor
recognizes the low probability of trans¬
mission errors by just ignoring parity.
The 920-B doesn’t (unless the user so
desires) since it might anytime get hooked
to a telephone line! It could easily con¬
nect via a modem to a timeshared system
such as MicroNet.
Comments on the SYM monitor
program. Like many other KIM-trained
machine-code programmers, I am keenly
aware of the beauty of both code¬
efficiency and time-efficiency. Also of
higher virtues of clarity, simplicity,
modularity, and generality. Hardly ever
are all of these wholly compatible.
The writers of the SYM monitor
were required to pack as much power
and versatility as possible into a 4K-
byte space (in a socketed 2332 ROM).
The coding gives priority to byte-saving
devices, sacrificing timing. They had to
complete the task quickly, at the cost of
incomplete testing. Version 1.0 had an
error in its KIM-format audio-cassette
program, corrected in a new version 1.1
ROM (that nonetheless had the log-in-
to-CRT flaw mentioned above). Its
high-speed audio-cassette interface
worked (in my hands) only with Micro-
sette or Data Sound data tape.
The SYM monitor has a command
language, similar in kind to that of KIM
but far more complex, and designed to
be easily user-expansible. I explored the
possibility of re-interpreting the key¬
board-command keys of the KIM in my
EDITHA program (DDJ #25; although
there are only 4 keys, anything one
may desire can be done by implementing
key sequences. However, the SYM ex¬
pects to interact with an ASCII key¬
board, so that a very large number of
single-key commands could be implemen¬
ted. Those that are recognized by the
monitor in its command-entry mode are:
B, C, D, E, F, G, LI, L2, LP, M, R, SI,
S2, SD, SP, V, and W. Six of the 2-
character commands (all but SD) deal
with loading and storing of programs with
audio cassette or paper tape. The others
are useful in program-writing, viewing,
running, and debugging (too esoteric
to go into detail). A command is ac¬
knowledged by displaying it and printing
a space. The monitor then shifts to a
hex-digit entry mode, that can accept
(and print) up to 3 sets of 4 hex digits,
delimited by a comma (or hyphen),
to serve as numerical parameters for the
command. Pressing the CR (carriage
return) key then causes execution if the
command is valid, i.e., interpretable by
the monitor. Only the M command is de¬
fined for all 4 parameter possibilities (0,
1, 2, or 3). If an undefined number of
parameters has been keyed-in, control
shifts to an “unrecognized syntax”
vector. An unrecognized command char¬
acter shifts control to a vector for that.
The computer elite (and some not-
so-elite) will naturally view a mere
command language as an antiquated
anachronism, when so many wondrous
high-level languages exist! I do some
reading in the HLL domain but see
nothing irresistably great there. A langu¬
age can imprison the mind. True, you
can encode complex logic in symbols that
may seem simple, and shift the arduous
task of programming and antibugging
machine code to an abler mind than your
own. But errors are instructive, tutelage
can dim vision, and few gains are not
balanced by (often unseen) losses.
A Preliminary Monitor-Enhancement
Program. The “unrecognized command”
mode is free-wheeling and congenial
for machine-linguists. In its command-
entry state, the SYM monitor is sent
any ASCII character it will not recognize.
It echoes this, and a space, then awaits 1,
2, or 3 four-digit hex parameters (more
could be had, but I prefer to limit com¬
plexity). I reserve the last one keyed
in for the address of the program to be
run. Therefore it is akin to the monitor’s
own G (for GO) command, except that
the user can provide parameters for the
program to use. The unrecognized-
command vector is reset to the address
of a simple 23-byte interpreter (INPRET,
cf. listings) that copies the second keyed-
in parameter to zero-page to serve as
an indirect address for program instruc¬
tions, then jumps-indirect to the last
meter to shift control to the program,
whose address is the real command.
The program in the listings is moderately
complex but not optimized (as much
of my earlier work was). It is an exer¬
cise in interaction between the SYM-1
and the 920-B, a sketch of something
useful that may become even more so,
perhaps even worth putting into an E-
PROM. I was driven to write it because
the SYM monitor expects to work with
“dumb” peripherals (or even with only
its own keyboard and hex display, in a
quite ingenious way). There is no provi¬
sion for teamwork with an intelligent
terminal, and its TTY-style programs for
displaying, modifying, and moving
memory are restrictive.
My new programs implement only
some of the possible intercommunication
between the SYM and the 920-B. While
this specific system may now be a unique
one, it may arouse some interest in the
teamwork concept, that is feasible for
any SBC working with any intelligent
terminal. The main program, DISPAG
(at $0C00 in the listings), is implemented
by the command sequence: T XYY,
ZZZZ, COO CR (where CR is the Carriage-
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 17
325
return key). Any unrecognized character
other than T works as well, since it will
shift control to the vector preset in
SA66D-E, that in the example is the
address of INPRET ($0D00). ZZZZ is the
starting address of the block of memory
to be displayed, e.g., COO will display the
program itself (note that leading zeroes
need not be keyed in.) YY is the hex
number of lines to be displayed, that
must range from 1 to $18. Any other
value will yield an error message and re¬
turn to monitor control. X controls the
display format, and need not be keyed
in if the “unispace” format is desired;
any hex digit from 1 to F will command
the “lister” format. This operation is
controlled by subroutined LNFORM,
that could be modified to allow other
formats.
The display will therefore be from 1 to
24 lines of bytes (as hex-digit pairs) of
memory. The first four (packed) hex
digits are the address of the first byte in
the line, separated by one space from the
byte sequence . In the unispace format,
each byte is followed by one space and
each line has exactly 16 bytes. In the
lister format, every opcode is preceded by
an extra space, so that the instruction
sequence is more legible. This is useful
only for programs, and is meaningless for
data tables. To avoid splitting one in¬
struction between two successive lines,
the lister format allows up to 18 bytes on
one line. It uses my old BYTCNT pro¬
gram, all-too-familiar to DDJ readers!
Parenthetically, I note that one more
6502 byte-count program, not very
efficient, has been published (BYTE, May
1980, p. 190).
When all the lines are displayed,
control shifts to the NEXCHR program.
This frees the 920-B keyboard for any
of its own programmed operations. To
return to the SYM monitor, the CR key
must be pressed twice in succession.
In this mode the display can be edited in
any way desired. Wholly new progams
can be created on the CRT screen.
NEXCHR merely echoes everything the
920-B sends to it, a mode that persists
unless a double-CR or a RUBOUT
signal is received. This last is a bit
dangerous, since it shifts control to a
progam sequence (starting at LNREAD)
that can wreck the SYM memory if used
carelessly. Its purpose is to transfer a
sequence of hex-bytes from the CRT
screen (really the 920-B memory) to a
specified region of the SYM memory. It
uses most of the code in the listings, and
was the trickiest to write.
For the 920-B to SYM transfer to
work correctly, the revised (or brand-
new) program on the screen must obey
the following restrictions:
1. Each line must start with 4 characters,
followed by a space. These will be read
but not used in any way. The reason for
this is to make it unnecessary to alter the
address information that DISPAG has
written, when an existing program is
being revised (or just moved to another
memory location.) It is an inconvenience
when a new program is being constructed,
unless the user wishes to keep track of
addresses, but at this early stage I prefer
not to augment the program complexity.
2. The lowest program line must be
followed by a completely blank line
(unless it is at the very bottom of the
screen display, in which case a blank line
will be automatically created by the
read operation). This is needed to termi¬
nate the transfer.
3. The line just above the first program
line must also start with 4 characters and
a space (again read but not used), and
then must have exactly 4 hex characters
that specify the SYM RAM address to
which the program is to be moved.
E.g., 0200 will cause transfer to start at
that location in the SYM RAM. The cursor
must be to the right of that address on
the screen when the RUBOUT key is
pressed. Since the top line provides the
only address information, this must be
correct!
It would be possible—perhaps desir¬
able—to include various anti-goof guards
(such as a requirement that the RUBOUT
key be pressed twice in succession to
initiate the transfer) but only use-ex¬
perience can truly dictate how a program
of this type ought to be refined. A few
guards do exist. Either a non-hex char¬
acter or an incomplete hex byte (only
one digit) will cause return to monitor
control.
The program lines need not be limited
to 16 bytes, or be written in any parti¬
cular format, though the lister format
is the most legible. When the transfer has
been completed, control shifts to the
VERIF program, that will use the DIS¬
PAG logic to display the revised or new
program that is now in the SYM memory,
and again shift to the NEXCHR mode.
This allows further revision, and another
transfer. This can be kept up until the
user is satisfied that the program is ready
to be tested. In my experience, it has
proved desirable to test tricky logic in the
form of subroutines, even when it will
ultimately be coded in-line to optimize
time-and code- efficiency. Debugging a
complex in-line program can be dif¬
ficult! There are times when I wonder
whether really adequate testing is even
possible. And is a poorly-tested program
really debugged?
The Game of ROM-Creation. Even
the minority of programmers who have
read the ROMs created by someone
else do not fully appreciate the problem
until they toy with the idea of creating
their own. It’s the chasm between critic
an artist, or rather between a builder of
sand-castles and a sculptor in marble.
My coding would surely seem very
sand-castly to the writer(s) of the SYM
monitor, who make heavy use of the
stack and hardly touch zero-page—while
I haven’t even one overt stack-save, and
transfer information freely via the on-
chip registers, and use zero-page with
wild abandon. The last is possible because
the monitor graciously cedes zero-page
to users, using instead its own half-page
of RAM staring at $A600. The only
zero-page locations it uses are the eight
of RAM starting at $A600. The only
zero-page locations it uses are the eight
from F8-FF. Its stack usage is compel¬
led by a seemingly iron rule that regi¬
sters must be saved and restored by all
subroutines, except when information is
to be returned in the accumulator, the
status register, or both. The 6502 in¬
struction set allows a 6-byte code se¬
quence for stack-saving (16 cycles)
and for restoring (20 cycles) its four
major registers PAXY. However, the
SYM monitor frequently saves bytes
by using a JSR SAVER (3 bytes but 103
cycles!) as the first instruction of a sub¬
routine. SAVER is an intricate 48-
byte program that rearranges the stack
so that, when it has returned, PAXY is
left on the stack. The subroutine that has
used SAVER exits by a JMP to one of
three entry-points of a program that will
restore all registers (29 cycles), only
AXY (41 cycles), or only XY (55 cycles)
before its RTS termination. This allows
three options with only six more bytes
added to the subroutine, but the timing
penalty is high (I think it’s why serial
transmission can’t exceed 4800 baud.)
The philosophic contrast shows in my
62 bytes of code from $0D2F in the
listings, that contain 13 different entry
points to a single RTS (and 2 others,
ESCOUT and TWOCHR, that are poten¬
tial entry points), averaging less than
5 code bytes per subroutine. This econo¬
my is possible only because nothing
is saved. Panegyrists of discipline might
also frown on the anarchy of my sub¬
routine LNFORM, that uses the Y
index for “parameter-passing” and PAX
in a self-centered way. Its calls to the
monitor subroutines OUTBYT and
SPACE, on the other hand, involve no
fewer than 28 stack save/restore in¬
structions, plus the musical-chairs stack
manipulation of the monitor’s SAVER
subroutine, for a total of 39 stack opera¬
tions! Since LNFORM only needs to pro¬
tect the X and Y registers from altera¬
tion by OUTBYT, OUTBYT does a lot
of work to svae LNFORM the 8 bytes it
would need to do it itself. The entire
KIM-1 monitor has only ten stack pull/
push opcodes, but does more saving
in zero-page—simpler but with the pos¬
sibility of conflict, that is of course a
powerful argument for using the stack.
Page 18
326
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
One thing is for sure. ROMs tend to time—much like one of the human lan- to be workable.” This means that some-
use a lot of subroutines. The KIM moni- guages—so there’ll be touches of awk- one must guess right the probability of
tor has 115 JSRs, and it’s the dominant ardness if one shifts to a less familiar set future events! Wow! In the saying per
opcode. The SYM monitor has 269 (or language), recognizable by a “native aspera ad astra, only the aspera are
JSRs (in twice the ROM space). Knowers speaker.” There’s also the “personal certainties,
of the 6502 will expect that the LDA style” factor, but some styles command
will be a close second (as it is in the KIM admiration even though they differ A Brief Afterthought on FORTH,
and probably in the SYM, that does not from one’s own. To me, FORTH has been the most tan-
have a static analysis of opcode usage A ROM also has an “architecture,” as talizing of the existing HLLs. Perhaps the
frequency). That is a powerful argument a CPU does, and this may be true of word is infuriating, since the FORTH
for speeding up subroutine calls, as the any program (even my rough sketch enthsiasts—like the Rosicrucians or the
lonely genius who designed the Signetics in the listings). The SYM ROM is basic- initiates to the ancient Eleusynian mys-
2650 years ago foresaw. I have no idea ally a comm and-language interpreter, tery — won’t tell you what it is. In com-
who he was (though I am sure the gender Having read the low-level “instruction,” parison, my own much more miniscule
is right), but I hope the story of the it first branches to one of the four “legal” programs come with a surfeit of ex-
2650 will someday be written, since fore- parameter-blocks (0, 1, 2, or 3 para- planatory comment (tinseled with allu-
sight is to me the most miraculous of meters). Each of these checks the “legal” sions). When I glanced at a listing of
all human qualities. I hardly need to command-characters and, if one is found, FORTH, its most striking quality was
expatiate, for readers of DDJ, on the shifts control to the proper execution the virtual absence of comment. Adam
virtues of subroutines: easy debugging, coding. If not, control shifts to the Osborne recently observed (InfoWorld
easy rewriting, and above all availability “unrecognized-command” vector, that 2(8):7, 1980) that the success of an
to any program. defaults to an error-message (very simple HLL depends less on its intrinsic merit
Re-reading my main program (from and clever). This is something more than thn on hhow hard it’s pushed. Whatever
$0C00 to 0C73), I see that I created a set of isolated routines filed so they the demerits of BASIC—and they are
seven subroutines, without quite knowing can be retrieved by keying the right legion-being unexplained is not one
why. All are used exactly once and could code, since the ensemble serves a com- of them. Dozens of books expound it
have been coded in-line. Why not? mon purpose. Perhaps the only compo- in great detail, and some are brilliant.
LNFORM CVHEX, and RNOSCP are nent of my new program that merits Where is the book that describes how
complex enough so that the need for addition to a monitor is the old BYTCNT FORTH works, from the ground up,
tailorability was perhaps subconsciously routine; all else is system-dependent, in a painstakingly detailed, translucent
obvious. The others are moronic drud- I am reminded of a brief—but highly an vivid way?
gery, and may just indicate something didactic —exposition of the principles of
like battle-fatigue. It’s wrong to assume system design (chapters 1 and 3 in the
that everything constructed by a frail book Systems Concepts, edited by R. F.
human being is a gem of purest ray Miles, Wiley-Interscience, 1973). A “sys-
serene! We get tired, we get fed-up, we tern” is defined as a large, complex,
don’t feel like recalculating relative- man-made set of concepts and/or ele-
branch offsets, so we do it the easy way. ments used to satisfy some human need.
This kind of feeling must have pervaded All components are integrated to yield
the SYM monitor-writer(s) near the end a set of optimum outputs from a set of
of the task. Michelangelo too, when he given inputs (some of them random,
put the finishing touches on the Sistine so that the exact performance at any
Chapel, at an age not far from my own. instant is unpredictable). It works semi¬
in fact, the subroutine-library concept automatically: machines always perform
that I lauded at the start of this com- some of the functions and human beings
munication is elusive. Who knows what always perform other functions. The
will be useful to many other workers? No design goal is to maximize “effectiveness”
monitor has a bytecount routine, but for a given cost—that implies trade-offs,
we now know it’s useful because so many I now shift from paraphrase to a key
have been created. The SYM provides a quotation: “Because it is generally impos-
block-move routine, that many KIM sible to find a single number which real-
users had to write for themselves. How- istically represents the effectiveness of a
ever, its byte-search program can only complex system, there is a good deal of
find single bytes (my EDITHA program subjectiveness, as represented by judg-
can also find sequences of two or three ment, as well as objectiveness, as repres-
bytes). What length of byte-string is sented by analysis, in systems engineer-
likely to be needed? ROM-design is ing.” The system is an entity such that
bedeviled by dilemmas, and is analogous "... optimization of each subsystem
to the design of the CPU itself, likewise independently will not lead in general to
frozen in silicon. a system optimum, and . .. improvement
One essential of ROM-design is mastery of a particular subsystem actually may
of the CPU instruction set. The SYM worsen the overall system.” Food for
monitor shows great skill in complex thought there! Less arguable is the con-
assembler logic, and is usually very well cept that “no system can be all things
coded, but there are spots where recod- to all people, all of the time” so that
ing would save both bytes and time. “the fundamental mission of a system
That kind of thing is rare in the work of should not be jeopardized, nor its funda-
Jim Butterfield, who “thinks in 6502”, mental objectives significantly compro-
so I assume that the SYM writer(s) learned mised, in order to accommodate events
on a different kind of machine. One gets of extremely low probability” since that
“conditioned” to a set one uses all the would make the system “too complex
Number 48 Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025 Page 19
327
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Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 21
329
PASTIMES
AND
PLEASURES
BY CHARLES WETHERELL
Structured Programming: Disease or Cure?
If you have spent much time around professional program¬
mers and their managers in the last five years, you have cer¬
tainly heard about structured programming. However, you
could be forgiven if you have not made up your mind whether
structured programming is a blessing or a curse. As a matter
of fact, you might well decide that structured programming is
some kind of disease.
The reason for your confusion could be the conversations
you had overheard. It is not uncommon to hear that over at
Impossibly Big Machines, Inc., they have just taken up struc¬
tured programming, said in tones suggesting that the company
should live through the attack. Or you might hear a project
leader from Completely Delerious Computing say thankfully
that he finally got his system out in spite of all those fancy
rules. Then again, you might go to a meeting trying to sell
your application package to Golf & Wasters, Inc. and be told
that it won t be considered unless every last IF statement is
indented just so. All of this suggests that structured program¬
ming is something like staphylococcus —it causes boils, but
it also can be turned into a valuable antibiotic.
The Source of the Confusion
A difficulty with the phrase “structured programming”
is that it describes a variety of activities, by no means all
comparable. First, structured programming is the name given
to the program synthesis tehcnhique developed by Dijkstra in
his book A Discipline of Programming (Prentice-Hall). This
method (and similar ones developed by others) aims at build¬
ing a provably correct program from a logical specification
of the program’s input and output relations. Two things
are required for Dijkstra’s structured program: a mathe¬
matical analysis of the programming language and consider¬
able mathematical sophistication on the part of the program¬
mer. When these requisites are available, Diskstra’s synthesis
can be very powerful, but it cannot be surprising that program¬
mers without the necessary training are overwhelmed and
bewildered by the heavy symbolism. Still, I can recommend
a look at Dijkstra’s book if only for the material on practical
programming.
Second, structured programming often refers generically to
a family of techniques for managing large programming pro¬
jects. Typically these techniques reduce the input and output
specifications of something like an inventory control system
to a standard format, a format that reveals the interdepend¬
encies and common needs of the system. Structured Analysis
and Design Technique, the Jackson Method, HIPO charts—
these are a few of the methods available. As might be ex¬
pected, these methods are not very useful to a programmer
working alone. Rather, they are more appropriate for mana¬
gers and planners in corporations and software houses.
Down to Earth
More appropriate to the programmer working alone is the
third meaning of structured programming. Here, the term
refers to the regulated and standardized analysis of a single
program. Top-down programming is nerhans the best known
technique of this type, but many methodical programmers
have their own home-brew structuring techniques. The ear¬
marks of a structured program are clean procedure interfaces,
well described data structures, straightforward control flow,
mnemonic variable names, ease of modification, and so
on. The good working programmer may already produce
programs like this, but structured programming is supposed
to increase the probability.
Finally, structured programming often refers to what I
call “structured coding.” This is the genesis of the canard
that structured programming is a blind book of rules governing
every comma and keyword. Actually, structured coding is
more like a newspaper style book. The purpose is to ensure a
uniformity of presentation in all programs. Further, best
solutions to common coding problems should be encapsulated
in the book so that each programmer need not redevelop
(at the programmer’s mental expense) the solutions. A good
style book does not inhibit a programmer’s expressiveness,
but it does make sure that his programs can be understood.
Page 22
330
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
Now we can see why there is such a mixed reaction to
structured programming. The manager thinks he has to be a
mathematical genius to understand it. The line programmer
is not very happy at having his creativity “managed.” Free
spirits don’t like any rules at all. And mathematicians don’t
program much anyway and can’t understand all the fuss.
Before I discuss how structured programming might apply
to you let me say that the proponents of the techniques I
have described might not all want to be lumped together.
But it is clear that in the minds of many computer people,
they have been lumped together. So when you hear structured
programming discussed in the future, you will at least be
able to decipher the conversation.
C*&-v
What Does Structured Programming Cure?
I assume that most of my readers are hobbyists and pro¬
gram for personal benefit. If that describes you, you may well
wonder how structured programming, thought up by academics
and industrialists to simplify the economical creation of
correct, efficient, maintainable programs, has anything to offer
you. Correct and efficient programs are always nice, but what
is this about economy and maintenance? Sounds like an ad for
an imported car. For the personal programmer, economy
means writing a program with as little psychic pain as possible.
And maintenance? An old philosopher once said that no man is
the same person after six months. In six months, though, the
new you is going to have to fix what the old you wrote; better
make the repair job as easy as possible. You would be surprised
how much you can forget about a program in six months.
And do you need to be programming in PL/I, COBOL,
ADA, or some other high-falutin language to use structured
programming? No, even in BASIC and assembly language,
structure pays off. My third and fourth meanings—standard¬
ized analysis and structured coding—can be applied to any
size program. We have all had experience beginning a new
program in a fever of creativity, writing and testing and de¬
bugging and modifying at top speed. What comes out of these
bouts? A program that works, but not one you would like to
work on. Generally, the result is badly commented, has
control flow that resembles a bowl of spaghetti, doesn’t work
on special cases, and gives readers hives. So back off and
rewrite. Use your own style, but do the job tidily. Build on
what you learned about how to do the program, but write the
program in a structured way. For this is the disease structured
programming cures. It cools brain fever.
Number 48
Dr. Dobb’s Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 23
331
Polymorphic Talks
to the Heath. HT4 Priptet
BY MARVIN KONOPIK
American Embassy
APO San Francisco 96503
Here is a short update to Marvin
Konopik’s article in DDJ #44,‘‘All The
Secrets You Ever Wanted About Poly
88 BASIC”:
I originally tried to warm start
the Editor at 2003, but it did not
work. As a result of my article in
DDJ, I was informed that 2003
was the location. I have retried it
and it does work.
My request for assistance in lo¬
cating the end of BASIC brought
many responses stating that 48AA
is the place to go. This would sim¬
plify the process of combining pro¬
grams drastically.
I purchased the Heath H-14 printer
after careful thought and meditation.
I certainly never assumed that my limited
background in electronics was sufficient
to contemplate building an interface to
connect a printer to a computer. Desper¬
ately in need of professional advice, I
called Heath to find out how hard it
would be to interface the two. Needless
to say, they said they were only con¬
cerned with Heath problems. This left
only me and the computer to solve the
problems.
Armed with determination and some
hard-earned cash, I ordered a printer,
waited out the delays until it arrived,
and began putting it together. It ran tests
with only a minimal amount of smoke.
The smoke seems to occur only as I be¬
come a more experienced Heathkit build¬
er. Actually Heath makes a very tho¬
rough, smoke-proof manual, but we
professionals seem to lose our ability
to read. There are three big questions
in this project. First, what kind of signal
is the computer putting out? Second,
did you make any mistakes in budding
the printer inputs? Third, with all of
those input wires, which ones will be
needed to do what? Since I did not have
an interface board, luck would be very
important.
As I stated above, I am not even close
to being an engineer, so the following is
probably not the right way to do the
job, but it worked for me. Give it your
best shot, and it might work for you. I
needed only 3 wires to make it go. You
will need a TTL/RS232 converter from
pin 1 (TXD), the computer out line, to
pin 5 (SIN), on the printer board. When
the printer is busy, it puts out a signal
on board pin 7 (RTS). This is a RS232
output, and must be converted to TTL
to talk to the computer. The RTS, con¬
nects to pin 4 (CTS) on the computer
board. The third wire is the ground, to
printer board pin 1. I made the TTL/
RS232 interface featured in a June 79
Kilobaud issue, for the SIN line, and then
that portion worked fine. But then the
printer was not able to keep up, and I
discovered I needed an RTS/CTS link
from the Printer to the Computer. I
used one of my already-procured spare
chips, which I buy automatically when
I get new equipment, and which is an
absolute necessity when you live over¬
seas. The printer uses two special In¬
tegrated Circuits. The 75189 (U103)
a RS232/TTL converter and the 75188
(U104), which is a TTL/RS232 converter.
75189 is ideal for use on the RTS line.
Had I known what the chips were for
in the beginning, I could have used the
75188 (U104) as well for the serial out¬
put. The easiest way is to buy the widely
advertised kit: however, a 7404 must be
used to invert the RTS/CTS signal.
Also had I known that the U103
and U104 were RS232/TTL and TTL/
RS232 converters, I would have certainly
tried for a shorter, simpler direct TTL
hookup, bypassing U103 and U104
completely. A 7400 would have provided
enough buffer power, with room left
over to invert the signal, if needed.
All that remains to getting it running
is the setting of the baud rates. Imagine
my surprise when I found that even
though the printer will work up to 9600
baud, it still prints at the same line speed.
A 9600 Baud printer at H-14 prices
would have not only been a definite
bargain, but it would be a real paper eater.
The high baud rates mean only that it
can load the printer with extra text much
faster. I found the 4800 baud rate just
seemed to work better, so I use that as
recommended by the Heath People.
But to make things more complicated,
I used an unorthodox signal cable. I
like things to go on and off with one
switch, so I put power and signal in the
same cable. Any engineer will tell you
that this is a real no-no, but it works for
me. If you do not have a plug to fit over
the printer board, one half of a 40 pin
dip socket works fine. I really felt guilty
not using all of those wires in the giant
cable Heath provides, and I know the
wires must be important or they would
not be there, but after hours of testing, I
just could not find a place to put them.
One wire will tell the computer that the
printer is not turned on. If the printer is
in the same room, this will be apparent
without wiring. Because of frequent
moves, my working comer changes size
and shapes quite regularly, so I decided
to try a worst-possible situation first.
I purchased a 20 foot soft cable to give
me later portability. A word of caution:
if you use the molex plug, be sure to keep
the signal and power wires separated and
insulated. One side of a molex plug has a
block that prevents reverse coupling.
It’s a little safer if you put the signal
wires on this blocked side to prevent
accidental contact if the plug is reversed,
and tipped in.
I had only minimal software problems.
The Poly 88 Editor worked super, but
BASIC was putting garbage on the line
during non-use. After days of frustration
and study of the Poly documentation,
I found that BASIC does indeed put out
garbage, in fact they call it JUNK. The
junk signal was a 7FH (DEL), which I
changed to 00H in location 4A7E and
the line was quiet.
Another discovery was the lost warm
start provision when using the Print
program. Warm start is bringing the com¬
puter up from reset, to restore not only
the BASIC, but the program previously
loaded in BASIC. Since BASIC and the
Print program were separate, and each
had their own starting locations, there
was no provision for bringing both up
warm. To use the printer program, the
procedure was to start it, and it will
in turn reach over and start BASIC.
But the start is cold, so I merely changed
that address, and it comes up warm every
time.
My printer printed columns a little
irregularly at first, but after a couple of
pages the rough edges wear off, and
the print quality, with the exception of
the funny little ‘g’s, is quite good. The
end result is really fantastic. It is hard
to imagine life without a printer, and the
HI4 is certainly one way to go.
*
Page 24
332
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
BY W. D. MAURER
George Washington University
S.E.A.S.
Washington, D.C. 20052
There are two kinds of indirect ad¬
dressing on the 6502, both of them with
indexing. Except for JMP, however, indi¬
rect addressing without indexing is not
provided. Since indirect addressing seems
to be more useful without indexing than
with it, many people have erroneously
regarded this as a design flaw.
In fact, anything you can do with in¬
direct addressing without indexing can be
done, and done faster, with post-indexed
(Y-register) indirect addressing on the
6502. We shall now give several illustra¬
tions of this.
Suppose we have two zero-page loca¬
tions called IA and IA+1 for holding an
indirect address. We can initialize these
by setting them to AD and AD+1, as fol¬
lows:
LDY AD
STY IA
LDY AD+1
STY IA+1
At this point we may do a JMP (IA),
but not a ST A (I A) (for example), since
that instruction does not exist on the
6502. It may be simulated, of course, by
loading the Y register with zero, so that
the full sequence becomes
LDY AD
STY IA
LDY AD+1
STY IA+1
LDY #0
STA (IA),Y
But this is unnecessary. All we have to do
is keep IA (the low-order address) set to
zero at all times, and write
LDY AD+1
STY IA+1
LDY AD
STA (IA),Y
which is a decrease in the number of in¬
structions (from 5 to 4), rather than an
increase (from 5 to 6).
Why does this work? Suppose that the
indirect address is 2345. Then AD con¬
tains 45 (hex) and AD+1 contains 23. In¬
stead of putting 45 in IA and 23 in IA+1
(giving an indirect address of 2345, with¬
out indexing), we put zero in IA and 23
in IA+1, giving an indirect address of
2300. To this we apply indexing, with 45
(hex) in the Y register; 2300 plus 45
makes 2345.
A common use of this capability is in
processing arrays of strings. Suppose we
have an array T of n strings, with n K 128.
This is implemented as an array of n ad¬
dresses, with T(2/c-1) and T(2 k) contain¬
ing, respectively, the low-order and high-
order parts of the address of the first
character of the k-th string in the string
array T, for 1 < k < n. To get the first
character of the k-th string, we perform
LDA K
ASL
TAY
LDA T-1,Y
STA IA+1
LDA T-2,Y
TAY
LDA (IA),Y
This assumes that T( 1) is contained at
T, T(2) at T+l, etc., so that T(2k-1) is
kept at T+2k-2 (= (T-2)+2k), and that
IA contains the constant zero as before.
This time the saving is not quite as great
because we cannot do an LDY T-2,Y di¬
rectly (we could not even do an LDY
T-2,X unless T is in page zero). But TAY
is certainly both shorter and faster than
STA IA (which is what we would have
done if indirect addressing without index¬
ing had been available). (Note: ASL, in
the above code, shifts the A register left
by one, thus multiplying it by 2. On some
assemblers one writes ASL A instead of
simply ASL for this.)
The same sort of savings accrue if T is
a parallel array rather than a serial array.
That is, suppose we keep two arrays, T1
and T2, where all the low-order bytes are
in T1 and all the high-order bytes are in
T2. That is, what was in T(2k-1) and
T(2/c), respectively, is now in Tl(k) and
T2(k). There is now no need to multiply
k by 2, and, perhaps more importantly,
we can have n < 256 rather than n < 128
as in the preceding example. (The reason
in both cases, of course, is that our
indices into the arrays T, Tl, and T2
must, in each case, fit into an eight-bit
register, and must therefore be between
0 and 255, inclusive. Arrays with this
property may be referred to as short ar¬
rays.) The code is now
LDY K
LDA T2-1.Y
STA IA+1
LDA Tl-l.Y
TAY
LDA (IA),Y
under the same assumptions as before.
In either case, incrementing the calcu¬
lated indirect address is also speeded up.
Incrementing the 16-bit quantity in IA
and IA+1, if we needed that, would have
been performed by
INC IA
BNE NXT
INC IA+1
NXT (next instruction)
In the actual case, the incrementation is
performed by
INY
BNE NXT2
INC IA+1
NXT2 (next instruction)
which is again both shorter and faster.
It is true that, in this case, if we know
that none of our strings has length greater
than 256, we can do even better by using
straightforward post-indexing rather than
simulated non-indexing. The setup takes
a little longer—we have to write some¬
thing like
LDA K
ASL
TAY
LDA T-1,Y
Page 26
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
333
STA IA2+1
LDA T-2,Y
STA IA2
LDY #0
LDA (IA2),Y
— but now a simple INY suffices for incre¬
menting the indirect address. Note that
we carefully set up two further page-zero
locations here, IA2 and IA2+1, because
IA2, unlike IA, is not kept at the con¬
stant value of zero.
Another, even more common, applica¬
tion of these ideas is in indexing long ar¬
rays (this is, arrays of more than 256
bytes). Suppose that U is such an array
and we wish to index U(J), where J has
just been calculated. Here both U and J
are 16-bit quantities. Assuming that #U
and /U represent, respectively, the (con¬
stant) lower half and upper half of the
address of U, we can add U and J and
store the result at IA2 by the following
code:
CLC
LDA #U
ADC J
STA IA2
LDA /U
ADC J+l
STA IA2+1
and then, if we had indirect addressing
without indexing, we would be ready to
apply it. As it is, all we have to write is
CLC
LDA #U
ADC J
TAY
LDA /U
ADC J+l
STA IA+1
with IA set permanently to zero as
before, and we are ready to use an in¬
struction like LDA (IA),Y (again, this
is both shorter and faster than what
preceded it).
If we can set aside another two bytes
in page zero for use only with this partic¬
ular array U, we can do even better than
that. Let us call them IA3 and IA3+1; the
permanent contents of IA3 are the low-
order byte of the address of U, rather
than zero. This can be set up with a de¬
claration like
1A3 ADR U
which actually sets up both I A3 and
IA3+1, although only IA3 will be needed.
We can now save two instructions each by
writing
CLC
LDA /U
ADC J+l
STA 1A3+1
LDY J
and now LDA (IA3),Y will load U(J)
into the A register. Why does that work?
Let us make the following abbreviations:
p — high-order byte of address of U (i.e.,
IV)
q — low-order byte of address of U (i.e.,
#U)
r - high-order byte of J (contents of loca¬
tion J+l)
s — low-order byte of J (contents of loca¬
tion J)
The 16-bit quantities we are adding are
256 p+q and 256r+s. The two bytes IA3
and IA3+1 contain, respectively, q and
p+r, so that this 16-bit quantity is
256 (p+r)+q. To this we add s by post¬
indexing, so that the computed address is
actually (256(p+r)+<j0+r = (256 p+q)+
(256r+s), or J plus the address of U.
The above may be extended immedi¬
ately to arrays U of two-byte or four-
byte quantities. A curious intermittent er¬
ror may arise, however, if three-byte
quantities are used. We would, of course,
multiply the 16-bit quantity in J and J+l
by 3 before using it, and then we would
increment Y by one (using INY) to get
the second byte set up, and again to get
the third byte set up. This works fine,
99% of the time. However, if J is 85, so
that 3J is 255, then incrementing Y by
one is not enough, since there is carry
into the high-order byte of 3J. We must
test for nonzero after the increment, and
then increment IA3+1 otherwise. (Similar
problems arise for J = 170, 341, 426,
etc.) It should not be hard to see that
there will never be carry of this kind for
an array of rc-byte quantities where n is
2, 4, 8, or in general any power of 2.
In the above case it was assumed that
U(0), rather than U(l), is contained at
U, if this is not the case, then the address
of U minus 1 must be substituted, in the
above, for the address of U. We assume
throughout, of course, that all 16-bit
quantities are kept with the low-order
byte first, as is customary on the 6502.
The concepts of serial and parallel array
are discussed further in [ 1 ]. Finally, users
of the LISA assembler for the 6502
should substitute $0, $1, and $2 for 0, 1,
and 2 respectively, throughout the coding
examples above.
Reference: Maurer, W.D., Programming,
Holden-Day, 1972, pp. 74-75.
About himself, Prof. Maurer has this
to say:
I’ve worked for CSC, Lockheed, Proj¬
ect MAC, UC Berkeley (as an Assistant
Professor) and The George Washington
University, Washington, D.C. (as an
Associate Professor and now a full Profes¬
sor). I've written a book called Program¬
ming as well as The Programmer’s Intro¬
duction to LISP and The Programmer’s
Introduction to SNOBOL. In my spare
time I write songs (My Pet Rock Is In
Love, Dracula’s Mood Ring, etc.) and
have them performed by a group of weird
people called The Hexagon Club.
LISTING
28
29
STA
LDY
IA
AD+*1
30
STY
IA+* 1
3PRINT ""
31
LDY
AD
!LOAD PPR5
32
LDA
#*37
BLOAI) PPR5, A*2000
33
STA
( IA), Y
OX!LIST
34
JSR
TS1
1
ORG
*18
35
LDA
#*11
2
ADR
U
36
STA
K
3
ORG
*0800
37
LDA
#P
4
LDA
#L2
38
STA
T+*20
5
STA
AD
39
STA
Tl+*10
6
LDA
/L2
40
LDA
/P
7
STA
AD+* 1
41
STA
T+*21
8
LDA
#*0
42
STA
T2+*10
9
STA
P
43
LDA
K
10
LDY
AD
44
ASL
11
STY
IA
45
TAY
12
LDY
AD+* 1
46
LDA
T-*l,Y
13
STY
IA+*1
47
STA
IA+*1
14
JMP
(IA)
48
LDA
T-*2,Y
15 L2
LDA
#P
49
TAY
16
STA
AD
50
LDA
(IA),Y
17
LDA
/P
51
CMP
#*0
18
STA
AD+* 1
52
EEO
L4
19
LDY
AD
53
BRK
20
STY
IA
54
L4
LDA
#*15
21
LDY
AD+*1
55
STA
P
22
STY
IA+*1
56
LDY
K
23
LDY
#*0
57
LDA
T2—*1,Y
24
LDA
#*37
58
STA
IA+*1
25
STA
(IA).Y
59
IDA
Tl-*1,Y
26
JSR
TS1
60
TAY
27
LDA
#*0
61
LDA
( IA),Y
Number 48
334
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 27
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Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
335
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Number 48
336
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 29
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Page 30
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
337
08E5-
8D
32 OF
STA
*0F32
090C-
6D
32 OF ADC
*0F32
A=51
X=00
Y=01
P=31 S=E3
A=83
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03
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33 OF
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A=0A
X=00
Y=83
P=70 S=E3
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14
LDA
#*14
0912-
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33 OF ADC
*0F33
A-14
X=00
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A~0D
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Y=83
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A—14
X=00
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18
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A"14
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32 OF
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6D
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ADC
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DO
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01
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18
CLC
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00
BRK
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A9
32
LDA
#*32
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X=00
Y=00
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0930-
A=
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Number 48
338
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 31
BY JOHN HOLTRICHTER, JR.
P. 0. Box 227
Redondo Beach, CA 90277
Dear Dr. Dobb's :
The Northstar BASIC Cross-Reference
Tool program written by Titus Purdin
and published in DDJ # 44 is not
designed to operate in a double density
system.
Since double density is now becoming
very popular, I thought your readers
might like to make the changes indicated
at the end of this letter in order to
implement the reading, in a double
density system, of single density type 2
files on single density diskettes, and both
single and double density files on double
density diskettes.
First of all, the routine should be
organized at 2D00H, and if it is wished
to be able to leave the program after
bringing it up but before naming a type 2
file, a CPI X and JZ EXIT should be
added to the INFILE routine, where X
may be 03H for a Control-C or 1BH if
an Escape is desired in order to return
x
o
§
£
a
2
2 a
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U I n
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h Q- N D- N
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co
aj
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CM
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cj
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immediately to DOS.
Since double density systems may
use up to four drives under versions 5.0
and later, a CPI 34H and JZ GETCR
should be added to the INUNT routine.
Next, the fact that, in the directory
sectors of the diskettes, the type of
file is listed with the 7th bit high in
double density and low in single density
formats, the CKTYP routine should be
modified and an additional single byte
storage location, DENS, must be defined.
In this modified routine, the type of file
is first checked to see if it is 02H (single
density type 2 file) or 82H (double
density type 2 file). In either case, only
the highest bit is saved in the DENS
location, where 00H = single density and
80H = double density.
The next problem to overcome is the
fact that in double density format, the
reading of a file using the DCOM routine
at 2022H in DOS provides 512 bytes to a
designated RAM address, while only 256
bytes is obtained in a single density
access of this routine. Accordingly, the
DATA storage location should be
increased in size to 512 in order to
accommodate a double density dump.
Now the routine which reads the
DATA area in RAM for processing must
be modified in accordance with the
density of the type 2 file to be investi¬
gated so that no more and no less than
the length of the data supplied with each
DCOM access is examined. The modifica¬
tion is made to the RDBL1 subroutine in
order to determine the density of the file,
and then to load into an expanded
BLKPT counter storage location (from
1 byte to 2 bytes long), 100H (256 bytes)
for single density or 200H (512 bytes) for
double density, in this initialization pro¬
cedure. Then, the Check Block Routine,
NXTCR is modified to load this 2 byte
counter value from BLKPT into the
H&L registers, decrement it, and then to
read the next block from the diskette file
into RAM, only if the counter has
reached zero.
In the following partial listing, some
presently existing code is shown to aid in
locating where changes and additions are
to be made.
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Page 32
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
339
ADDENDUM
Dear Editor:
Thank you for your kind letter
of April 21 concerning the publica¬
tion of my changes to Titus
Purdin’s X-Ref program.
The reason for my previous com¬
ments was that I run both double
and single density North Star and
CP/M systems in my IMSAI 8080
(Z-80 CPU) and the changes were
needed in order to allow me to best
utilize this fine tool. However, I
also run both 80 X 24 and 64 X 16
formated monitors (along with four
5 l A inch and four 8 inch drives) and
I find that the X-Ref program was
designed for only the 80 X 24
format, which makes it difficult to
read the last of the eight columns
on the smaller formated screen.
I can also see where this format
would cause problems with those
who have printers that cannot
accommodate 80 characters on a
line. Accordingly, I have set forth
below a simple solution which may
be incorporated as a post script to
my previous letter, if you wish.
In the subroutine labeled
‘LSTN1the MVI A,8 should be
changed to MVI A,7 for a 64 char¬
acter line, and MVI A,4 for a 40
character line. The former change
will provide seven groups of line
numbers per line, while the latter
will provide four groups per line.
Nothing will be lost, but the
columns will become longer. The
purest may also wish to shorten
the dedicated length of PLINE: and
the number of blanks (20H)
deposited therein, etc., but the
saving in program length will be
minimal.
LSTN1 XRA A
STA TAB
MVI A.7 ;7=64 CHAR’S/LINE: 4=40 CHAR S/LINE
STA L1NCT
I have also noticed that the
program, as it stands, will not work
in systems which check the A
register to see which input device
is being used. An example of this is
the standard North *Star Horizon
system. A solution to this problem
is to add MVI A,0 for the standard
input device (video terminal) and a
1, 2 or 3 etc., for other input
devices, immediately before a
CALL CIN. The locations of these
additions are as follows:
INFIL: MVI A.O ; 0-STANDARD VIDEO TERMINAL
CALL CIN
INUNT:
LXI H,DRIVE
MVI A,0 . 0=STANDARD
CALL CIN
GETCR: ANI 0FH
MOV M.A
MVI A.O 0-STANDARD
CALL CIN
The same general procedure
should be followed (placing device
number in the A register) before
calling COUT, if the output is to go
to a device other than the video
terminal. For example, a 1 would
send the output to a line printer.
Number 48
340
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 33
HARDCOPY D€nce DRIUCR PROGRAM*? FOR CP/m
BY STEVE WILLOUGHBY
Owner, W.E.D.
Box 87
Crane, Indiana 47522
812-854-7434
The following programs were written
to add a flexible hardcopy output to a
CP/M system. These programs may be
coresident (i.e. punch tape and print on
tty and also print on daisywheel printer).
The hardware consists of a processor
with 32K bytes of contiguous low
read/write memory, (RAM, with 4 K
bytes of RAM at D000, a serial inter¬
face wherein RS-232 pin 20 (Data
terminal ready) disables transmit buffer
empty (TBMT) status to allow high speed
transfers with buffered printers by hand¬
shaking through DTR. The software
shown uses the same interface for both
devices, so these routines would not
logically be coresident without changing
one interface assignment.
Each program consists of a relocator
which uses the CP/M jump vector at 0
to locate the active BIOS jump table,
retrieves the current jump link addresses,
punches them into the driver program,
relocates it to its place of residence,
alters the CP/M BIOS jump table entries
to point to new driver, performs initiali¬
zation of device and driver, and reboots
CP/M.
My system has aVDM and parallel
keyboard for the system console. When
the driver program is run (as any other
CAM file), the device becomes the
system printer and console output is
intercepted and printed, or not, depend¬
ing on the position of the associated
sense switch. If additional drivers are run,
the last one is the system printer, all
others being lost; however, the console
output print/no print is stacked up
through each successive driver. The
Diablo driver also has provisions to re¬
place the parallel keyboard by the serial
keyboard of the diablo printer..
Caution!!! If a driver program is run
twice it will lock everything up; if run
immediately after itself, it will return
to itself after the output; if run at any
other time (intervening drive(s) run)
it overwrites the valid CONOUT return
and forms a loop through the intervening
drivers.
For those who don’t have sense swit¬
ches: write a CONIN intercept routine
to intercept normal keyboard input.
If a control P (CDOS convention) is
detected, complement a location. This end of the page, prints a cut mark ( — )
location would then be read instead of between two blank lines. A count of char-
sense switches. The control P could be acters per line is maintained and an auto-
passed along or suppressed (not recom- matic CR/LF is generated to prevent
mended.) overprinting. Tabs are expanded to spaces
No longer does your console output and occur at positions exactly divisible
scroll off the screen to oblivion, yet by 8. A form feed mark routine is done,
neither are you a slave to pulpmills and All other control characters are ignored,
slow printers when hard copy is not (Thrown away.)
needed. You have hardcopy of listings, The daisywheel printer must have its
DDP disassemblies, ED text while in e- tab stops preset by a character stream,
ditor, and system journal when you It recognizes form feed, and does not
can’t stay and watch things grind. require delay after CR. The printer re¬
ceives commands in the print stream with
DEVICE PECULIARITIES: The teletype- escape sequences, of which is added two
writer is of the kind that has no tabs, no to allow resetting the carriage and top of
top of forms, and needs a delay after form (Esc — R/r) and reset the tabls
carriage return, and overprints at the end (Esc - T/t).
of the line. The programs are highly commented
This routine counts lines and, at the and should be self-explanatory.
?
AljTYPE DIABLO.PRN
DIABLO 1650 I/O DRIVER FOR CP/M
Revision level 2.1 2-28-80
Steve Willoughby
Box 87
Crane,IN 47522
D400
i
DESTIN
EQU
0D400H
(Driver destination address
0004
*
STATUS
EQU
04H
(Status port
0080
MASK
EQU
8 OH
(Printer ready bit
0040
INMASK
EQU
4 OH
(Keyboard ready bit
0005
PORT
EQU
05H
(Printer port
0000
SENSE
EQU
00H
(Sense of data
0004
JSENSE
EQU
04H
(Sense of status
0001
SEN SWT
EQU
01H
(Sense switch port
0002
SENMSK
EQU
02H
(Printer on bit
0004
KEYMSK
EQU
04H
[Keyboard substitute bit
0000
SENSEN
EQU
00H
[Sense of switch register
0100
START
ORG
100H
0100
317F00
LXI
SP,7FH
(Set up stack
0103
2A0100
LHLD
0001H
[Get warm boot address
0106
110400
LXI
D, 04H
[Point to console status link
0109
19
DAD
D
010A
E5
PUSH
H
(Save constatus address
010B
7E
MOV
A,M
[Put it in program
010C
321B02
STA
CON1+1
010F
23
INX
H
0110
7E
MOV
A,M
0111
321C02
STA
CON1+2
0114
23
INX
H
(Step to conin link
0115
23
INX
H
0116
7E
MOV
A,M
(Get conin link
0117
320702
STA
CON2+1
011A
23
INX
H
01 IB
7E
MOV
A,M
one
320802
STA
CON2+2
Page 34
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
341
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344
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 37
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BY G. GAUGLER
5706 Seascape Ct.
Citrus Heights, CA 95610
The enclosed listing is an assembly
language (PDP-11) version of a program
I originally saw in BASIC somewhere.
The program was interesting, not terri¬
bly useful, and quite slow. However,
this is exactly the kind of program one
needs when trying to demonstrate a com¬
puter sytem to a non-computer person.
I have found it rather successful for
nocturnal social acquaintances, etc. U-
sually they would lose interest by the
time the BASIC version would finish.
This implementation will be as fast as
the output device. An obvious advantage
in such situations.
The fundamental principle of the pro¬
gram could be extended to other types
of figures or drawings. The byte table
contains the counts of characters and
spaces (blanks) in an alternating order.
A byte with the sign bit set (hence a
negative quantity) indicates that the
count is for characters at the far left of
the figure; meaning that it starts a new
row. The next byte would be the count
of spaces. The following byte would be
for the count of characters, and so on
until another negative byte is found or a
zero byte. The zero byte signals the end
of the table.
The program prompts for a characters
string which will be impressed into the
figure. Character positions are preserved
across blank fields (as can be seen in the
enclosed example).
For any interested readers, I also have
the same program coded in 6800 assembly
language. A SASE will prompt me to send
it to anyone who wants it.
Page 38
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
345
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Number 48
346
Dr. Dobb’s Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 39
Page 40
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
347
A PROBLEM WITH
LOGIC PROBES
BY DAVID N. BERTOLLO
89 Westdale Avenue
Hillsdale, NJ 07842
ABSTRACT
While debugging a TTL system using
the Micronta Model 22-300 ‘'multi-logic
compatable ” digital logic probe, I discov¬
ered that this probe will only give a cor¬
rect high level logic indication in fifty
percent of the cases of a true TTL logic
high. A TTL circuit is herein described
which will operate properly when testing
TTL logic levels.
The Problem
A few months ago, while debugging a
new Z80 system, I decided a digital logic
probe would be useful to have and
that it would be much easier to purchase
such a probe than to design and build one
from scratch. Several digital logic probes
are available from a number of manufac¬
turers, ranging in price from $25-100.
On the surface, it appeared that the
higher the probe’s cost, the lower the
value received. In the end, I decided to
purchase the $25 variety: a Micronta
22-300. It seemed that this probe would
suffice for all but a few fast pulse points
in the system for which it would be used
(the probe cannot indicate a pulse of
under 300 nano-seconds duration). This
probe also had the advantage of being
advertised as working with several logic
families.
After spending several hours trying to
diagnose the ills of the new Z80 system
with the Micronta probe, it seemed that
more of the Z80’s data lines were in an
open state than seemed reasonable. Being
suspicious of the probe, I studied the por¬
tion of the probe’s user manual devoted
to verifying the probe’s correct operation.
Using the test set-up shown, I determined
that a logic low was being indicated for
voltages of from 0 to 1.8 volts, and a
logic high for inputs of 3.4 through 5
volts. Input voltages of 1.8 through 3.4
indicated an open condition. The manual
indicated that these levels should be
within 30 percent and 70 percent of Vcc
and with an error range of ten percent.
As a Vcc of five volts was being used, the
proper voltages should be 0 through 1.5
for a logic low indication, 3.5 through 5
volts for a logic high indication, and 1.5
through 3.5 for an open indication. Thus,
the probe appeared to be operating with¬
in the manufacturers specifications.
Wondering whether all those data lines
were in their open state after all, I con¬
sulted a specification sheet for a 7400
TTL NAND gate. This told the story. A
TTL logic low is defined as 0 through 0.8
volts and a logic high is defined as 2.4
through 5 volts. Further, a typical TTL
gate will produce an output of between
3.3 and 5 volts. Therefore, fifty percent
of all good TTL outputs will test properly
with the Micronta probe; the other fifty
percent, although perfectly good as far
as TTL logic levels are concerned, will
show up on this probe as opens.
In order to see if the Micronta’s opera¬
tions were typical of multi-family logic
probes, I examined the specification sheet
for the Heathkit TTL/CMOS digital logic
probe (model 7410). When in TTL mode,
this probe will indicate a logic zero for
voltages of 0 through 0.8 volts and a logic
high for voltages of 2.1 through 5 volts.
When in CMOS mode, zero through thirty
percent of Vcc gives a logic low; while
seventy to one hundred percent of Vcc
give a logic high indication.
Apparently, the Micronta probe will
only operate properly with CMOS logic,
even though it is advertised as having
“multi-logic compatibility.” In actuality,
the only TTL compatibility this probe
has is accidental.
At this point, three options were avail¬
able: 1) Purchase a new probe, such as
the one from Heathkit; 2) Modify the
Micronta probe to operate properly with
TTL logic levels; and, 3) Design and build
a new probe for TTL logic.
As I did not desire to spend money on
another logic probe, option 1 was quickly
discarded. The Micronta probe did not
come with a schematic. Having no love
for tracing the probe’s circuit, option 2
was swiftly discarded. This left only op¬
tion 3.
Circuit Description
The circuit for the new probe is shown
in the Figure. It uses two inexpensive TTL
chips, 1 diode (for polarity protection),
two capacitors, three LED’s and 3 resis¬
tors: a total cost of under $3 for parts
(less a case to house them). This probe
will resolve TTL levels properly, and will
also detect pulses as fast as 40 nano¬
seconds. Its two disadvantages are that it
may only be used for testing TTL logic
and it will not detect an open line condi¬
tion (which will show up as a logic high).
The first hex inverter provides one
TTL load to the circuit under test. In¬
verter stages two and three drive the high
and low level LED logic state indicators.
IC2 serves as a pulse stretcher. Any nega¬
tive transition on the input line results in
an output pulse of about 150 milli¬
seconds, which lights the LED pulse indi
cator. For pulse trains slower than about
seven pulses per second, the indicator will
blink on and off. For faster pulse trains,
the indicator will stay on continuously.
For single pulses, it will blink once.
In order to make the indicators easier
to differentiate, a red LED was used for
the logic high indicator, a green LED for
the logic low indicator and an amber (yel¬
low) LED for the pulse indicator. The cir¬
cuit was housed in the Micronta case,
with the Micronta’s innards now living in
the junk box waiting for the day a CMOS
logic probe is needed. As only a small
number of components were required,
the dead bug method of construction was
used (i.e., the two IC’s were glued to one
side of the case, with direct solder con¬
nections made to their exposed pins).
Conclusion
Using the new TTL logic probe, those
open state data lines were not open after
all, the processor clock was no longer
clocking and those 40 nano-second
pulses looked fine. Within ten minutes of
using the new probe, the Z80 processor
was starting to respond to instructions;
within four hours it was fully opera¬
tional.
David Bertollo is a senior programmer
for Information Sciences Division,
Rockland Research Institute, Orangeburg,
NY. He is involved in the development of
both applications and systems programs
for a network of mini computers feeding
a maxi host computer. Before rebirth as a
programmer, he was an electronics design
engineer. -SR
(Continued on pg. 45)
Page 42 Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025 Number 48
348
To enable a program or operating system to verify and
correct errors in the pointer links of linked record chains, a
redundant set of links is necessary. This compact method
uses a ‘forward’ link from each record to its successor record,
and a ‘cross’ link, which is the XOR product of the previous
record address and the successor record address. These two
links are stored in each record. With a typical disk sectoring
arrangement, they should probably be stored at opposite
ends of the record, to minimize effects of recording medium
flaws.
The major advantage of this method, compared to direct
forward and backward links, which take the same space in
each record, is that this algorithm can determine which link
is wrong, and can correct it. Every record contains, in effect,
two independent forward pointers (one based on the know¬
ledge of the previous record address), and a back pointer (the
XOR of the two links).
Because of the asymmetry of these links, verification and
correction is best done during forward sequencing through the
chain. Verification consists of:
Determine the next record address by XORing the
previous record address with the cross link in the current
record. This should be identical with the forward link in
the current record.
(Note that the XOR of any two of the above values should
be equal to the third one. The procedure above yields an
alternate successor address, if it is needed).
If the test fails, either the forward link or the cross link is
wrong. The error can be corrected by examining both possible
successor records, to determine which points back to the cur¬
rent record containing the error. The XOR result of the for¬
ward link and the cross link in the successor record should
be the address of the current record. If one of the two tested
successor records points back to the current record, the er¬
roneous link is changed to point to that successor record.
If the cross link is wrong, it is reconstructed by XORing the
previous record address with the correct successor record
address.
In the first record of a chain, the forward and cross links
are equal, so their XOR result is 0. The logical address of the
first element of a chain therefore must be non-zero, since the
“previous address” is 0. In the last record, the forward link
is 0, and the cross link is equal to the previous record address.
Correction of links in the last record is a special case; if one
successor address is 0, the non-zero successor record is exam¬
ined to determine whether it points to the current record.
If it does not, the current record is the end of a chain.
This link verification and correction algorithm can be done
“on the fly” during any file read or write operations, so that
randomly caused errors in the links can be routinely cor¬
rected without any error messages or significant overhead.
No extra disk accesses are needed, except when an error is
found
LINKS.N
Number 48
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 43
349
m > /> o
’ /UU
ip |i jif m /
addend
M
BY DENNIS ALLISON
Many software systems need some
sort of a symbol table. A symbol table is
simply a mechanism which associates a
name with some information. A name
can be a string or a number. Normally
one expects the space of possible names
to be represented as much, much larger
than the number of table entries. Further,
there is usually a premium placed on
finding entries efficiently.
Just what kind of mechanism is best
for any particular application will depend
upon the way the table is to be used
and what information is to be stored
in it. Let’s presume we have an applica¬
tion where the entries are of fixed size
and deletions will not be made. An
assembler is one such application. The
data can be represented by a structure of
the form:
struct |
char name [8j ;
int val;
i symtab [256] ;
One could, of course, fill this table
from its first entry and determine wheth¬
er a key is present by searching for it
linearly. If nentries is the number of
entries in the table, and match is a
predicate function which returns non¬
zero if the keys match and zero if they
do not, then one can search the table
with the code:
lookup ( key ) char * key ; j
int i;
for(i=0;i<nentries;i++) j
if(match(key, symtab[i] .name)
return (i) ;
/* here only if fail * /
return ( -1 );
!
Here we have chosen to return the value
— 1 if the entry is not in the table. The
average number of matches for an entry
in the table is nentries /2 and the re¬
quired number of matches to determine
an entry is not in the table is nentries.
We can improve upon this considerably.
For this particular situation a closed
hashing scheme is effective. We provide a
special function, hash which maps the
key into an integer between 0 and 255.
This function is chosen so that, on the
average, for any large set of names all
values will be generated the same number
of times. As there are many more than
256 possible names, there is no guarantee
that the hash value of two names which
are themselves different is not the same.
The lookup algorithm then proceeds
as follows: First, hash the key and find
an index into the table. If the key
matches the name stored at that location,
we have found the entry. If the slot in the
table is empty, the key does not appear
in the table. Often, as we do below, the
key is entered into the table at this point
and the table index returned. If neither
of these conditions hold, one must ap¬
peal to a collision resolution strategy.
This key potentially hashes to the same
value as some other table entry.
The traditional collision resolution
strategy is to search the table linearly
forward (or backward) modulo the table
size. This is simple but tends to produce
dense clusters of entries which degrades
performance.
The scheme I like uses some properties
of residue arithmetic and depends upon
the table size being a power of two.
An auxiliary counter is used which allows
one to generate a sequence of values
which steps through every element of the
table, but the order of search is dif¬
ferent for every initial value. This helps
prevent clustering and improves the
performance of the table. The particular
algorithm used here was published by
F. R. A. Hopgood and J. Davenport
in The Computer Journal (15:4, No¬
vember 1972). See their article for a dis¬
cussion of the theory involved.
A program which implements their
algorithm is:
lookup (key) char *key; j
int i, j;
i = hash(key); /* value is 0 to 255 */
j = 1; /* used for collision resolution */
for (;;) /* infinite loop */
/* test for empty */ .
if(sym [i] .name[0] == ’ ’ )i
scopy (key, sy m [ i ]. name);
return (i) ;
I
/* test for match */
if (match (key, sym [i] .name ))
return (i); /* found it */
/* resolve a collision & test for full */
i=(i+j)& OxFF; .
if ((j = (j + l)&0xFF)==0) |
error (“symbol table overflow”);
return (-1) ;
t
(
(
The function scopy copies the key into
the designated table location. The logical-
and operations are used to provide effi¬
cient arithmetic modulo the table size.
Performance of this particular table is
very good when it is only partially full.
When the table is less than 70% full,
entries which are present can be found
with an average of three probes. As
the table fills, the performance will
eventually degrade to a linear search,
but full utilization of the storage space
will be made.
There remains the problem of choos¬
ing the initial hash function. What one
wants is to ensure that the information
is spread pretty uniformly. One would
like the string “ab” to generate a dif¬
ferent hash than the string “ba.” Lastly,
one wants the operation to be efficient
to implement.
One possibility is
hash (name) char *name; j
int v,i;
v = 0;
for (i=0;i<8;i++M
v = v + v — *name++;
retumtffv^^S)+v) & OxFF);
This function gives fairly good results.
On a base of 5000 words it gave fre¬
quency values ranging from 10 to 43
about two-thirds in the range of 15
to 24.
Now that we’ve got a mechanism like
this, we can make a dandy little program
which counts instances of words. We need
Page 44
350
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
a procedure to fill the key array, call
it getword. It reads a word from a file
and places it in the buffer pointed to by
it’s argument. It returns non-zero as long
as the buffer is valid, that is, as long as
the end of the file has not been reached.
The main part of the program becomes
wordcount () j
char the word [ 8 ] ;
while ( gotwoid ( the word ) )
sym [lookup (the word) ] ;
sym [ i ] .val);
}
etters
THE DEBATE ON TOP-DOWN CONTINUES
Dear DDJ:
In DDJ #43 I stated that top-down programming is
easy in COBOL but impossible in PASCAL. Mr. David
Rowland contests this admittedly provocative statement
(DDJ# 46). He challenges me to define top-down program¬
ming in a way that excludes PASCAL and to defend that de¬
finition in a multi-lingual environment.
Top-down programming is an approach to programming
that results in a particular structure in the finished product.
The process of “stepwise refinement” cited by Mr. Rowland
should be reflected in three ways: in the logic flow of the pro¬
gram, in the physical structure of the source listing and m the
sequence of preparing and testing modules.
Necessarily, a program prepared by the top-down method
is both modular and hierarchical. There is a main module
where the program begins and ends. There are subordinate
modules called by it. These may in turn call still lower level
modules and so on to as many levels of hierarchy as the com¬
plexity of the task requires. There are also (in the real world)
some little utility modules that are called all over the place
and hence to not really fit anywhere in the hierarachy. In very
large programs (compilers, operating systems) we may be deal¬
ing with hundreds of modules written by dozens of program¬
mers.
I will use as an example a short program consisting of a
main routine 000 which calls modules 100, 200, 300 and 400.
Module 100 calls modules 110, 120 and 130. Module 200
calls modules 210 and 220 and so on. The program also uses
utility routines 900, 910 and 920.
Proceeding in top-down fashion, after the general structure
of the program has been roughed out we write module 000.
We then write the modules subordinate to it, proceeding from
left to right and from top to bottom in the hierarchical se¬
quence of the program. After the main line module is written,
there are two acceptable sequences for writing the remainder
of the program. Usually it is best to sequence the program
level by level. Our example program might be written thus:
ooo
100
200
300
400
110
120
130
210
220
310
320
330
340
410
(900)
(910)
(920)
Some programmers would find it convenient to put the 900
series modules early in the program, perhaps just after 000.
The second common sequence is the indented order. It
is useful if the programmer likes to pursue a particular func¬
tion to completion before proceeding further. It is also used
where either the programmer or the operating system is going
to do overlays to save memory space:
ooo
(900)
(910)
(920)
100
110
120
130
200
210
220
300
310
320
330
340
400
410
Note that the physical sequence of the modules is also the
order in which they are written. Note also that the whole
program is not written at one sitting. There are compilers
for errors and test executions early in the life of the program.
Modules called but not yet written are inserted as “dummy”
routines.
Now let me offer a nonsensical sequencing of the same pro¬
gram, given our top-down approach to its construction:
900
910
920
110
120
130
210
220
310
320
330
340
410
100
200
300
400
000
This is the sequencing required by PASCAL, XPL and most
other languages designed for use as teaching tools. In this class
of languages a procedure must be defined before it is called.
The main routine that should be written first must occur
last in the source listing. Given a program of non-trivial
dimensions this is an almost impossibly clumsy way to pro¬
ceed. It also makes the finished program very hard to read
since you must start near the end and jump around in the list¬
ing to follow the source text in any logical sequence.
Bottoms-up sequencing makes sense if you are writing an
extensible language. It also allows implementation of a simple
“one-pass” compiler. But for the serious programmer who
is trying to produce a good product within a reasonable
time span it is a miserable restriction. I have never seen a top-
down program written in any commercial language that did
not also order the program in a top-down sequence, with the
main line routine first, followed by its subordinate routines
in one of the two acceptable sequences described earlier.
Languages such as COBOL, FORTRAN, PL/I and even most
assemblers allow top-down sequencing of source code. PAS¬
CAL, unfortunately, does not.
I stated three ways in which the stepwise refinement and
top-down programming approach should be reflected: in the
physical sequence of program text, and the order of progam
Number 48
352
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Page 49
development and of course in the logic structure of the pro¬
gram. PASCAL prohibits the first and thereby inhibits the se¬
cond. I stand by my earlier assertion. Top-down programming
as I understand the term is virtually impossible in a language
that requires a bottoms-up sequencing of source modules. Mr.
Rowland feels that he programs top-down “on (his) best
days.” I understand how difficult this must be in an inherently
bottoms-up langauge like PASCAL, and I offer him my sym¬
pathy. In my experience, languages developed as classroom
tools usually do not make good production languages. There
are too many restrictions (such as the bottoms-up sequencing
of PASCAL) which make sense only in the classroom. Indeed
I question the utility of “upside down programming” even in
an academic environment. Perhaps some knowledgeable
reader can enlighten me on this issue.
Sincerely, 2401 Haight Avenue
John R. Culleton, Jr. Sykesville, Maryland 21784
Page 50
Dr. Dobb's Journal of Computer Calisthenics and Orthodontia, Box E, Menlo Park, CA 94025
Number 48
353
Dr. DoBB'S loURNALof
COMPUTER
(Calisthenics ^ Orthodontia
Running Light Without Overbyte
Number 49 October 1980 Volume 5, Issue 9
A REFERENCE JOURNAL FOR USERS OF SMALL COMPUTERS
Even Further with Tiny BASIC 4
Robert Hudson
CP/M To UCSD PASCAL File Conversion 16
Tor Sjgwall
Extended Source-Text Area and Label Capability for SC/MP NIBASM 20
W.F. Long
MFT: A Multiple File Transfer Utility 24
Lawrence E. Hughes
A Cross Reference Program for Northstar BASIC 32
Larry Hudson
and more ...
355
Even Further With
tiny BASIC
BY ROBERT HUDSON
1315 August Drive
Austin, TX 78753
No —not full floating point math, which is unnecessary for
a control language or string functions; but extended —yes,
indeed. The original Tiny BASIC for the Motorola 6800
as implemented by Pittman is an extremely small (2K) and
powerful BASIC ideally suited for a minimum system or
control application. The original Tiny BASIC has the following
commands:
LET var GOTO expr REM
IF ... THEN GOSUB expr CLEAR
INPUT var RETURN LIST
PRINT END RUN
Variable Names A — Z.
Operators:
+ Addition
— Subtraction
* Multiplication
/ Division
() Parentheses
Functions:
RND
USR
Relational Operators:
= Equality
< Less than
> Greater than or equal to
<= Less than or equal to
>= Greater than or equal to
<> Not equal
As illustrated above, Tom Pittman has performed a fantas¬
tic feat of programming, considering the interpreter only re¬
quires 2K bytes. You may wonder what extensions are pos¬
sible for such a colorful and rich minimum implementation of
BASIC.
My extensions are: Logicals:
SET AND
SET& OR
GET NOT
GET&
CHR
NEW (CLEAR)
INPUT “TEXT”” var
FRE
The above extensions require only an additional 128 bytes of
memory.
Tiny BASIC was originally a concept of Dennis Allison’s
and was actually the foundation which helped to create Dr.
Dobb’s Journal. The first few issues of Dr. Dobb’s covered
the theory of the tiny interpreters. I became intrigued with
Tiny about a year ago, but had time to delve into it only
recently. What really intrigued me were the two levels of
interpretation. By this I mean the tiny BASIC interpreter
is written in an Intermediate Language (IL), not machine code.
The Intermediate Language is interpreted (read and decoded)
by machine language routines. And since the IL is well defined
with operation codes and addressing schemes, all the user has
to do to change, alter, or add to a particular version is to re¬
define the IL program.
In Figure 1 is a program written in MITS 6800 BASIC
(written by MICROSOFT). The program is an assembler for
the IL code of Tiny BASIC. Because I did want the ability to
redefine, expand and enhance Tiny, I had to write the as¬
sembler to facilitate this. This was necessitated mainly because
the IL relies heaviliy on relative addressing. A great help in
understanding the operation and mnemonics of the IL pro¬
gram was a book published by Tom Pittman, “Tiny BASIC
Experimenter’s Kit,” which sells for about $15. If anyone
wishes to pursue experimenting with Tiny and Pittman’s IL
program, then this book is a must. In the book Pittman
has an assembler for Tiny IL code written in Tiny BASIC,
but it was inadequate for my needs. Therefore, I developed
my own assembler. In the book Pittman completely explains
the operation codes and the addressing modes.
Also included in this article is a listing of the assembled
enhanced Tiny BASIC IL code to implement the above
additional functions. This can be found in Figure 2. In Figure
3 is a 6800 assembler listing of the machine language routines
necessary to implement some of the additional functions.
In Figure 4 is a hexadecimal memory dump of the installed
enhanced IL interpreter.
I will briefly explain these:
IL BASIC ASSEMBLER PROGRAM (Figure 1)
A two-pass assembler, the first pass being necessary to re¬
solve forward referenced labels. The source code file is part
of the program being stored in DATA statements. A leading
“*” asterisk indicates a comment line. A leading “>” greater
than indicates a label. The source file is stored from line 90
to line 840. Following the source file are a group of DATA
statements which define the operation codes of the Tiny IL.
The main program loop is entered at line 1030 where an
option menu is presented. “Assembler pass 1” must be se¬
lected first, followed by “Assembler pass 2”. Pass 2 generates
a .paginated listing as can be seen in Figure 2. The assembler
has complete error trapping c»«cpt for tiro “SJO 1 op - — t «
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 4
356
Number 49
This op code normally has a maximum argument of 7. I de¬
cided not to check the argument in order to facilitate imple¬
mentation of new op codes. Also the mnemonic for jump was
changed from “J” to “JP”, therefore making all the op codes
the same length. The only other alteration necessary was with
the circumflex or up-arrow. This is normally used to generate
ASCII control codes by subtracting 64 from the preceding
character—this is implemented. However, because I store the
source file as DATA statements it was not possible to use
the comma in a source line of code because my BASIC
interprets the comma as a delimiter in the DATA statement.
I therefore used the circumflex to also generate the necessary
ASCII code for the comma (lower case L— 64 = 44). The same
is also true of the colon I had to use the lower case Z.
This brings up an interesting point also, in the IL code the
symbol is used in conjunction with the circumflex to
generate the ASCII null code. There was a slight problem with
this because my BASIC interprets the symbol as an input
line delete code. Because of this the user will find in line 70
four POKE commands which are used to NO OP the area
of the BASIC interpreter (KCBASIC) which honors the
as the input line delete code. Therefore, if, when using a
similar but different BASIC **please**, delete this line or
change the POKE addresses to agree with your BASIC.
ASSEMBLER OUTPUT (Figure 2)
The BASIC Assembler program produces a titled and pagi¬
nated listing of the assembled IL code. The listing is complete,
even including the error code numbers which are generated
by incorrect operation. The listing provides a self documenta¬
tion of the TINY IL code. After assembly the IL code is com¬
pletely position independent and only one pointer need be
changed to point to the new IL code. In other words, one
may have several IL interpreters in a computer at one time
and switch back and forth between them just by changing a
pointer to the beginning of the IL code desired.
Changes and Extensions:
Prompt Character — changed from a colon “: ” to the
greater than symbol “ > ”.
New — the “CLEAR” command was changed to “NEW”
to agree with other common BASIC interpreters.
SET — stores a one byte word in memory.
Syntax: SET address expression = expression
SET& — stores a two byte word in memory.
Syntax: SET& address expression = expression
GET — returns the value of a one byte word from memory.
Syntax: GET (address expression)
GET& — returns the value of two bytes from memory.
Syntax: GET& (address expression)
CHR= — outputs the ASCII character indicated by the
evaluation of an expression. If the expression is greater than
255 then output is mod 256.
Syntax: CHR= expression
INPUT — now allows an optional text string to be printed.
Syntax: INPUT “text” variable
FRE — returns the number of bytes remaining in memory
in which a program can be stored.
Syntax: PRINT FRE
Logicals:
AND — returns the 16 bit results of a logical AND opera¬
tion between the two arguments.
Syntax: AND (first expression, second expression)
OR — returns the 16 bit results of a logical OR operation
between the two arguments.
Syntax: OR (first expression, second expression)
NOT — returns the 16 bit complement of the argument.
Syntax: NOT (expression)
MACHINE LANGUAGE ROUTINES REQUIRED (Figure 3)
Machine language routines had to be written in 6800 code
to implement the logical operators and also the two byte
commands (SET& and GET&). The other commands were
implemented without additional machine language routines
being necessary. However, the following is very important
for custom installation and understanding.
SET uses the built-in POKE function located at 0118
HEX. This should be the same for all Tiny BASICS. GET
uses the built in PEEK function located at 0114 HEX. This
should also be the same for all Tiny BASICs.
CHR bypasses the regular output routine in Tiny and
goes directly to your system output routine. The address
which points to your output routine should be inserted on line
37 of the IL listing (Figure 2). Since my system is not MIK-
BUG, this address currently points to my output routine. All
that is necessary is to change the source code to LN 265 which
will produce IL code of 0A0109. Location 0109 being the
tiny BASIC jump to the character output routines in MIKBUG.
FRE was implemented wtihout any problem. However,
for other Tiny BASICs using different MPUs the storage loca¬
tions for the limits of memory may be different. As can be
seen in the IL listing (Figure 2) for the 6800 version these
are defined as 34 HEX and 36 HEX in lines 224 and 226.
Logical functions are defined in the IL code (Figure 2)
from line 196 to 213. They call the appropriate machine
language routines as found in Figure 3.
INSTALLATION
Load your Tiny BASIC by Tom Pittman. Now using your
system’s appropriate memory change and examine commands,
enter the code found in Figure 4 starting at 07A1 HEX. This
will overlay the previous IL code with the new IL code.
Change location 07F2 HEX from 07 92 to 01 09. This will
permit the CHR function to use your output routines which
location 0109 HEX should be pointing to.
Now change the breakpoint jump located at 010C HEX
to contain 097A HEX. Add at 097A HEX the following:
7E 07 6A 7E 07 8D.
Now change the following pointers in the Tiny BASIC
program:
location 01FE HEX change to 07 BC-points to IL code
beginning
location 0201 HEX change to 09 08 - points to program storage.
This concludes the installation procedure. Now begin the Tiny
BASIC interpreter at 0100 HEX and have fun.
REFERENCES
1. TINY BASIC User’s Manual. Available from ITTY BITTY COM-
puters, P.O. Box 32189, San Jose, CA 95153.
2. Doctor Dobb’s Journal, Volume I, No. 7
3. TINY BASIC Experimenter’s Kit. Available from ITTY BITTY
COMPUTERS, P.O. Box 23189, San Jose, CA 95153.
LISTING
Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 5
357
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
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Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 7
359
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360
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
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Number 49
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 9
361
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362
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 9402S
Number 49
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Number 49
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 11
363
Microcomputers
... as they should be [
BY OLAV NAESS
Welhavensgt. 65
Bergen, Norway
The microcomputer has great potental for interacting with
the real world as well as for expanding into a large computer
system by addition of various storage units, computing units,
interface units, etc.
But the microcomputer systems of today are far from able
to realize the potential for interfacing and expansion, or at
least they implement such potential in an unnecessarily awk¬
ward way. It seems to me that the main reason for this is bad
mechanical design. The mechanical problems evidently tend
to escape attention. I will therefore try to throw some light
upon these problems, and suggest solutions for them. The
intention behind this article is to create widespread dissatis¬
faction with present designs, so that those with powers to
bring about such reforms will be induced to get moving.
Now, let’s take a look at the common mechanical design of
a non-trivial microcomputer, i.e., one that can be expanded to
a multi-module system. The modules, each normally one PC
(printed circuit) card, are usually plugged into connectors
which are situated in fixed positions on a rigid motherboard,
and the whole assembly is mounted in a box. The box is a
typical afterthought. It does protect the cards against dust
and damage, but also hinders more constructive interaction be¬
tween the computer and its environment. The few simple
controls and connectors that can be placed on the edge of a
PC card are difficult to use when the computer is on, even if
the cabinet is opened.
Cables to the outer world must find their way out of some
opening in a rather disorderly manner, and heaven knows what
traumatic experience the modules are exposed to as some
creature passing by in the external world gets entangled in one
of the cables.
In my own mixed X-100 system, the keyboard communi¬
cates with the internal video terminal card through a flat cable
that plugs into DIL (dual in-line; IC) sockets on each unit’s
PC card. There was obviously no standard for such a connec¬
tion, so I had to identify the signal lines and resolder one of
the DIL plugs. The crossing wires on this plug made it impossi¬
ble to close its lid, which had to be left floating over the plug.
If the keyboard is moved, the flat cable sweeps over the com¬
ponents of the video card. Disconnection of the keyboard
necessitates opening the computer’s cabinet, unplugging the
video card, and then carefully wriggling that fragile DIL
plug out of its socket. Those who enjoy dancing with an oc¬
topus can try to move the computer system while the external
units are connected.
On the top of the video card sits an edge connector to
whose solder lugs various other external connections are sol¬
dered, amongst them the video cable! This thick, rigid coaxial
cable should certainly not be allowed to sweep across the in¬
terior of a computer and exert its powers upon some poor
little solder lugs. Breaks and shorts have again and again caused
a blank screen in my system. Conclusion: Video cables can
only be connected with (coaxial) connectors properly
mounted on a rigid external surface. Letting external con¬
nections go directly to the PC card is a dubious practice.
More thoroughly designed computers employ cable assem¬
blies divided into an internal and external cable, the two meet¬
ing in a connector pair on a cabinet surface. This is safe and
covenient, but an expensive solution which also imposes
restrictions upon the types and number of connectors that
can be used.
Is there any solution to our dilemma? Yes, and module
systems with the desired properties are even commonly used in
all sorts of laboratories. A PC card for such a system has a
narrow plate mounted vertically on the card, running along
the card edge that is opposite to the edge connector. When the
cards are plugged into the system’s frontless enclosure, these
narrow plates, whose two ends may be screwed directly to the
enclosure, constitute a front panel. All connectors, switches,
indicators, etc., needed by a module may thus be mounted on
the module’s own piece of front panel, and their connections
with the PC card can be short and fixed.
This packaging system does, however, still have some an¬
noying shortcomings: the enclosure has a fixed size which is
quite likely to be too small or too large. And modules are not
accessible for testing and adjustments unless they are un¬
plugged.
I will therefore suggest a further improvement: the front
panel plate should go all the way around the PC card, as shown
in Figure 1 and further illustrated in Figure 2. That is: the
cards are mounted in frames which are attached to each other
by separable hinges. When end-plates are hinged to the first
and last module, the modules are completely enclosed: no
space is wasted, and the enclosure can be expanded to any
size. Such an assembly can be opened like a book during oper¬
ation for testing or adjustments.
A hinged-frame microcomputer, which could have frames
designed to hold S-100 cards, should have a flexible mother¬
board passing inside the hinged edges (which might be detach¬
able from the side edges, too). Such a motherboard would
restrict expandability somewhat, but the unused part could
run along one or both endplates. Modules hinged together this
way may be virtually anything from a framed PC card to large
units like a power supply, a disk drive or even a video monitor.
A frame for PC cards could have several small cards mounted
side by side —useful for sub-modules with perhaps just one
LSI IC. Heat-generating components could be mounted in
perforated frames, and circuits requiring screening could have
screening plates adjacent to their frames.
Page 12
364
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
Figure 1. Hinged frames with PC cards, and one detached
end plate.
Figure 2. Section of frame-mounted PC card with controls
and flat cable connections.
Frame-mounted cards are less vulnerable when removed
from the system than unmounted cards are. If frame dimen¬
sions are standardized, cooperating systems like a computer
and an audio system can be merged to a single unit.
Figure 3 shows what a large hinged-frame system may look
like. The keyboard (in a wedge-shaped module) is here opened
180 degrees relative to the next module.
A small computer may have just one or a few thin modules
just below the keyboard module, and resemble a TRS-80.
If the user of such a small computer wanted to use control
panels designed for special applications, he could mount them
like a PC card in a frame anywhere in the computer.
Imagine sitting down in your easy-chair with your book¬
like microcomputer in your lap. You leaf through pages of
control panels until you find one for a game you would like
to play . ..
Enough about the enclosure; now let us look at the external
cables and how signals are allocated in them.
Regarding external connections, there prevails an unfortu¬
nate tendency towards unnecessary splitting-up; by using
separate cable assemblies for the various types of signals and
power, and by splitting multiplexed (bus) signals into separate
digital ports or analog channels at a too central site. The circu¬
itry required for decoding/latching signals from a bus is cheap
compared with a decent cable assembly. A universal I/O bus
which can be extended out into the real world can greatly
increase the controlling power of the computer, decrease costs,
and decrease confusion caused by lack of standardization.
The IEEE-488 bus is such a bus for peripheral units but is
too specialized. Besides, its communication protocol is rather
complex.
To illustrate my notion of universality, I would like to de¬
scribe a universal I/O bus system I have just constructed. It
communicates through a 25-conductor flat cable with stand¬
ard DB25 connectors, but a stackable connector would be
preferable. The conductors carry:
1: Power from the computer: 5 V stabilized. 8V and ±18
V unstabilized, plus ground.
2. The 2 MHz clock from the X-100 bus.
3: Two analog lines: Output from a D/A converter and input
to an A/D converter (placed between filtered power lines).
4: Count and gate inputs to two counter-timers (Intel 8253).
5: An interrupt input.
6: An 8-bit digital data/address bus with control lines.
(CLOCK, ADDRESS COMES)
Even though hundreds of external units can be addressed,
the I/O system occupies only a sequence of four ordinary
I/O ports:
First port: Address of the external unit (output).
Second port: Data to/from the external digital data bus.
Third port: Least significant byte to the D/A converter or
from the A/D converter.
Fourth port: Most significant byte to the D/A converter or
from the A/D converter.
Figure 3. Small computer made up from hinged-frame
modules has one cabinet rather than four.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
Page 13
365
(Continued from page 13.)
Ports required for the counter/timer and any interrupt
controller are additional.
To operate the bus, an I/O transfer is initiated by output¬
ting an external address through the first p ort. When this one-
byte address goes out the external bus, the ADDRESS COMES
line goes active (low), and CLOCK goes active (high). This
activates the external address decoders and loads shift registers
associated with these address decoders. Each parallel output
of these shift registers will activate an input or output data
transfer if it has a 0 (low). When an address decoder reports
an address match, it loads a 0 into a certain shift register bit.
All the other shift registers along the bus are filled with non¬
activating 1 ’s. The transfer activated by a 0 may be in or out,
digital or analog:
Digital in: An eight bit tri-state buffer puts its data on the
external bus.
Analog in: An analog switch connects an analog input to the
analog input line.
Digital out: An eight bit latch takes data from the external
bus.
Analog out: A sample-and-hold circuit samples the analog
output line (analog outputs need periodic refreshing).
Between each such external transfer the data byte is read
or written through the second, third, or fourth port. Immedi¬
ately after an I/O through the second or fourth port, a pulse
emitted on the CLOCK line causes a shift in all the peripheral
shift registers (with a 1 -bit entering), so that the next transfer
is activated by the 0-bit in the active shift register (besides,
an A/D conversion is started).
The external address can indicate the entrypoint anywhere
in a sequence of assorted-type transfers. Because time-con¬
suming processes like A/D conversion and stabilization of long
signal lines occur between the computer’s I/O-operations, the
computer is never forced to wait provided the intervals be¬
tween I/O-operations don’t become too short, like during
DMA bursts.
Well, folks: if these things sound interesting, don’t expect
real products or properly tested designs to come from an
amateur like me. I can only hope that manufacturers can be
enticed to move along such lines, and that they will establish
useful standards.
Page 14
366
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
BY TOR SJ0WALL
G-15
N-7035 Moholt
Norway “
CP/M TO UCSD PASCAL EEIttEE
-— file conversion
We were all very pleased with the article on PASCAL to
CP/M file conversion in Dr. Dobb’s, but there is also a need
to go the other way; to use CP/M 2.0 files in the PASCAL II.0
environment.
In order to get at the CP/M files, you have to access the
diskette on a direct track/sector basis because of the differ¬
ence betweeen CP/M and PASCAL file formats. This is not
possible under the PASCAL system as described in UCSD’s
manual but there is something they have not told us about
the UNITREAD and UNITWRITE intrinsic procedures. The
parameters to these procedures are according to the manual:
procedure UNITREAD (unitnumber, array, length, block-
number integer);
Unitnumber integer name of an I/O device
Array packed array for transfer
Length number of bytes to transfer
Blocknumber absolute PASCAL block number on a diskette
Integer optional (1 indicates async transfer)
Disassembly shows that the integer parameter has more op¬
tions
Values may be added to combine options.
4 & 8 only workonCONSOLE:, PRINTER: and REMOUT:.
Direct track/sector I/O do not use the ordinary block-
number parameter. Instead a blocknumber is calculated as:
track: 0 . . 76 ; sector : 1 . . 26 ;
blocknumber : = (track * 26) + (sector — 1);
NOTE: Length parameter is ignored
Array parameter has to be at least 128 bytes (1 sector)
IORESULT is never set, always 0
I don’t know if this option will work on all PASCAL
systems, but it is likely since it is the only way to get at the
bootloader on the diskette. The P2-code interpreter addresses
in our implementation are: unitwrite 22A8H and unitread
22ADH, with direct option at 230CH.
The GETCPM program uses the direct sector option to con¬
vert CP/M textfiles to PASCAL .TEXT files. Datafile con¬
version is also supported. Random access CP/M files are not
properly converted, but this is easily implemented in COPY-
PAGE by sending IK of null or space when cpmpage=0.
1. Asynchronous I/O, not implemented in our 8080 system
2. Direct track/sector diskette I/O
4. Text file indent code expansion on output activated
8. Automatic linefeed append after return
Tor Sjowall is a student at the Norwegian Institute of
Technology who will soon be a professional engineer. Tor
works mostly on microcomputer systems but his main field
is digital switching in telephone networks.
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Page 16
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
367
Number 49
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
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Page 18 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 Number 49
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Number 49
370
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 19
Extended Source-Text Area
and
Label Capability for
SC/MP NIBASM
BY W. F. LONG
Naval Medical Research Institute
Bethesda, Maryland 20014
Are you using Roger Marin’s SC/MP assembler (SL0060) written in NIBL BASIC 1 ?
Would you like to be able to expand the source-text RAM area beyond one 4K page
for larger programs? Do you find that 26 labels aren’t enough or that you need to
begin two with the same alphabetic character? If you answered “yes,” read on.
The following modifications are simple and brief. Together, they affect four exist¬
ing lines and add one new line. Separately, the two extensions affect different lines
and do not interact. They may be added singly if desired.
Expanded NIBASM reads source text across any allowable number of 4K pages
consecutively from the starting address. (NIBL defines page 7 as the upper limit and
you must remember to save space for generated object code.) Label capacity is dou¬
bled by permission of the entire lower-case alphabet as beginning characters.
Source-Text Area Expansion
Existing program line 120 begins the text search for each line of source:
120X=«L*256+«<L+1 >: N=L+4: IF<X=-1 >OR(W=4!>PR" ": PR"END RSM": END
where variable L points to the current line number stored in NIBL format; N is the
text cursor; and W is the pass counter. In the first statement, variable X is set to the
current line number converted from base 16 to base 10. The first test in statement
three looks for X equal to the NIBL program-page-end flag. A true result terminates
the assembler.
Program line 120 is rewritten to cross 4K page boundaries with NIBASM:
120X=«L*256+«<L+l>:N=L+4:IF«CL+2>=#FF L=<#0FFF OR L>+3:GOTO120
where the conditional portion of the line has been replaced. Now the test is for a new
user-set flag in the byte following the two line-number-storage locations. If the flag
tests true, variable L is advanced to the first line-number address of the following
RAM page, and line 120 is re-interpreted with the new L value.
New line 130 tests for source-text end with the omitted portion of old line 120:
1301F<X=-1 >OR■;W=4>PR" ": PR"END RSM": END
NIBL shares the new NIBASM user-flag position described above without inter¬
ference NIBL uses it within program text as the line length indicator, storing a maxi¬
mum possible value of 48H. At program-page end, it is the address of the NIBL
function TOP.
Label Capacity Expansion
Original NIBASM scratchpad-RAM occupies the top 200 bytes of page 1, from
IF 38H to 1FFFH. The label-table takes 52 bytes (2 bytes per upper-case alphabetic
character) from 1F3EH to 1F71H. Variable I is designated the label-table pointer in
program line 20:
20PR "SC-'MP ASM":PR"OBJCT CODE RflM="j:INPUTD:H=S100:1=7993sW=1
where 7998 is the first character-A address in base 10. All but the last two statements
of line 30 comprise a label-table initialization loop:
30FORX=0TO51:«<I+X>=#FF:NEXTX:U=8050: 2=-l
Page 20
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
371
After the first statement of line 200 normalizes the beginning character value of a
suspected label, statement two tests character nonvalidity:
200X=<«N-65'.>*2: IF<X<0JOR<X>50>GOTO220
where N is the text cursor; X is set to the normalized character value; and a nonvalid
character is outside the range of capitals A through Z.
To double label capacity, one must double the label-table. But, what about the
first six scratchpad bytes 1F38H to 1F3DH used elsewhere by NIBASM? Six special
ASCII characters separate the two alphabetic cases. If label-table pointer I is moved
lower in memory by twice the number of lower-case and special ASCII characters
combined, a version of the original label text/storage method can be devised that will
skip over those original first-six scratchpad bytes. New program line 20 reflects the
altered label-table pointer, I:
20PR " SC ■•’TIP ASM" : PR"OBJCT CODE RAM=" INPUTD: H=8100: 1=7934: W= 1
The modified second statement in line 200 still tests for character nonvalidity:
200X= < «N-65 > *2:IF < X< 0 > OR < X >50 > AND <X<64>0R(X>114> GOTO220
Lower-case alpha characters are no longer invalid, however, while the six special
ASCII characters remain invalid.
Now when unmodified program line 210 indexes from pointer I by normalized
valid-character X to store the label value, lower-case labels are stored in the original
upper-case table. Upper-case labels now occupy the new scratchpad range 1EFEH
though 1F31H, automatically skipping the originally allocated first six bytes (six
free scratchpad bytes from 1F32H to 1F37H are also created.)
Label-table initialization adjustment is all that remains. An added loop-statement
to program line 30 accesses the original table area by indexing from the new pointer-1
address:
30FORX=0TO51:«<I+X>=#FF:NEXTX:
F0RX=64T0115:« <1+X > =#FF:NEXTX: '3=8050:2=-1
The old loop is retained for initialization of the new table.
Using Expanded NIBASM
When writing source for expanded NIBASM, you may include the entire lower¬
case alphabet as beginning characters in 26 extra labels, while otherwise following
Roger Marin’s original rules.
Following the final source entry on a page, enter an immediate statement of the
form:
JSTOP*tr. HH
where hh = FF when source to be assembled with the current page is contained on the
next higher page or where hh = any lower value when assembly is not to be continued
across a page boundary.
There are no other procedural differences between original and expanded NIBASM.
Incorporating the Modifications
Assuming packed entry, the source area expansion changes add 42 bytes to the
original program. The label capacity expansion changes add 48 bytes. Either modifica¬
tion will fit if entered alone without further packing of Roger Marin’s NIBASM
source. NIBL may flag AREA ERROR during combined inclusion however.
Packing is one optimizing technique for interpreted programs. A line is read and
executed more quickly when it contains no unnecessary characters or spaces. Packed
text also allows more program within a given memory space.
Original NIBASM is well-packed as published. Still, I reduced its total size by 71
bytes as copied into my system. All eliminated bytes were spaces. Probably a reduc¬
tion by half that amount would comfortably accommodate both modifications.
Addendum
I have just executed a test assembly with Expanded NIBASM on source text con¬
taining all SC/MP mnemonic/pointer permutations. This test assembly uncovered the
only “bug” I’ve been able to find in the original program. The last statement on line
4525 tests the assembled opcode value in order to flag two-byte instructions for
further processing. Unfortunately, the value tested for “greater-than” is the DELAY
intruction opcode (mnemonic DLY), so the instruction is assembled incorrectly.
The “bug” can be fixed by changing the test reference value from #8F to #8E.
Acknowledgment
Naval Medical Research and Develop¬
ment Command, Work Unit No. MF58.
524.015.0018. The opinions and asser¬
tions contained herein are the private
ones of the writer and are not to be
construed as official or reflecting the view
of the Navy Department or the Naval
Service at large.
Footnote
1 Both NIBL BASIC and NIBASM
are available from NSC’s user group:
Compute/5226, National Semiconductor
Corp., 2900 Semiconductor Dr., Santa
Clara, CA 95051. SL0042A, NIBL-N —
paper tape, SL0060, NIBASM —Listing.
Mr. Long accumulated 10 years of
hardware experience in design,
development modification, fabrica¬
tion, and repair of analog and
digital medical research instrumen¬
tation for the Naval Medical Re¬
search Institute before including
microprocessors and software 2-14
years ago.
Number 49
372
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 21
BY H. T. GORDON
College of Natural Resources
University of California
Berkeley, CA 94720
In an elementary essay on micro¬
processor instruction sets ( Kilobaud
Microcomputing, March and April, 1980),
I tried to “read” the complex minds of
the elite few who design them. Although
I have met in person (too briefly for
significant interaction) only two of them,
I was not surprised to learn that they
comprehend instantaneously not only a
question but its implications (in my
experience, a rare thing). But I know
them by their work, unquestionably great
art, as I know Aeschylus, or the architects
of the great cathedrals of Bourges and
Chartres, or certain poets who have used
the more elusive constructs of English or
German. As Juliet says, what’s in a name?
What matters is the profound structural
diversity of human minds — and the
possibility of symbolic intercommunica¬
tion not restricted by time or space.
This prolegomenon has served only as
a “signature,” and I shall now lapse into
rationality. The rational purpose of this
note is to explore in depth a problem
lightly touched on in my Kilobaud essay:
how can one create, for an 8-bit CPU,
more than the 256 possible one-byte
opcodes? It is well-known that the Z-80
was the first design to use a “leading
byte” (one of four different bit-patterns
unused by the 8080) to endow the next
byte with an utterly different meaning
(from what it would have had standing-
alone). The effect is to create 1024
possible two-byte codes, most of them
not defined at the higher level of Z-80
assembler language. It is not surprising
that the CPU circuitry nonetheless “runs”
many of the undefined codes (cf. the
letter by D. R. Lunsford, DDJ #44). The
6502 also runs most of its undefined
(one-byte) opcodes, some as “nopcodes”
(cf. my note in DDJ # 28, p. 29). I
assume that it would complicate the
microcircuitry if designers tried to
“block” this (as big CPUs now do).
Designers probably see undefined codes
as a “reserve” that could be used for new
instructions. In fact, the brief preview of
the 6516 by David Kemp (BYTE, May
1979, p. 213) states that this upgrade will
define the 105 8-bit opcodes not defined
in the 6502 set. It also implies that the
6516 will go no further. That’s a tenable
position, but I wonder. The turmoil in
the 6502 upgrade is indeed great (so
much so that Chuck Peddle quit for a
while!) but there are not enough bright
people involved so that the number 256
cannot be an uncrossable limit. In reality,
the limit must be already crossed, since
the 6516 is not likely to discard the
“decimal mode” status bit of the 6502.
This bit, when set, redefines the 6502
arithmetic opcodes from binary to
decimal operation.
We have now struck the alternative to
the “leading byte” concept: the “ninth-
bit” expansion (that the Signetics 2650,
with its two status registers, uses very
freely). This kind of expansion has its
peculiar trade-offs. For example, if a
programmer needs only one decimal-
arithmetic instruction, this must be
preceded by an SED (becoming in effect
a two-byte opcode) and should be
followed by a CLD to cancel the effect
(effectively three opcode bytes!). How¬
ever, the (one-byte) arithmetic opcode is
normally inside the loop, and the two bit-
control codes are outside. If the loop
iterates the arithmetic code 20 times,
the overall effect is to create a “1.1 byte”
opcode with faster execution. Were it
done by a “leading-byte,” the program
would have to load forty bytes during
execution instead of only 22. On the
other hand, since a “leading byte” is a
one-time control, there is no need for an
extra program byte to cancel its effect,
and there may be less chance of error by
careless programmers. The 6502 decimal
bit does not, of course, eliminate a
leading opcode byte, but the following
“decimal-adjust” byte used to decimalize
arithmetic instructions in most designs.
However you look at it, no design creates
a set of one-byte decimal arithmetic
opcodes. Most use what is in effect a two-
byte opcode to convert the binary arith¬
metic codes to decimal operation. This
means they cannot have dual-purpose
arithmetic programs, as the 6502 can,
since the same program can be made to
work either in binary or decimal
depending on whether the decimal bit
is set or reset before the call.
In my Microcomputing article
(accepted by then-editor John Craig early
in 1978) I express admiration for the
2650 and the belief that future designs
will be influenced by its many innova¬
tions. In fact, the 6809 did adopt its
flexible status-bit control, and its pro-
gram-counter-relative addressing mode.
However, this pioneer third-generation
chip rejected the “ninth-bit” concept
and imitated the Z-80 by creating multi¬
byte opcodes. Since the 6809 is based on
a lot of thought (cf. BYTE, Jan. 1979,
p. 14), this would seem to be a strong
argument against the “ninth-bit” ap¬
proach, that is not even mentioned
in the BYTE presentation of the 6809.
The brief discussion of “design decisions”
for the 6809 does not say who made
these decisions that to me sound like
restrictions ( I must emphasize that I
am not acquainted with any of the
restrictors or restrictees in this case, but I
assume the universality of restriction.)
One can speculate that Motorola execu¬
tives imposed restrictions, and try to read
their minds! It is my vague impression
that these “practical” men fostered
(tolerated?) the radical imaginings of
Chuck Peddle that are the 6800, in the
hope of overcoming the early lead of the
8080. They were justifiably annoyed
when it did not, and perhaps surprised
when Peddle’s more advanced creation
(the 6502) turned out to be an effective
competitor. Since an obvious strength of
the 6502 is its many addressing modes,
and the success of the Z-80 could to
some extent be attributed to enhanced
addressing, a sure-fire response would be
to endow the 6809 with vastly superior
addressing power. This needs lots of
opcodes! Since the Z-80 had succeeded
with multibyte codes, while the 2650 had
got nowhere with its “ninth-bits,”
practicality would demand “leading-
Page 22
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
373
byte” solutions. The way of the pioneer
is hard, and the 6809 shows signs of
having left room for maneuvering beyond
its “play-safe” philosophy, should any of
its coming rivals include some spectacular
innovation. It retains both one-byte and
two-byte undefined opcodes. If you have
lots of opcodes, and the only value of a
“ninth-bit” is to economize on one-byte
codes,, why bother with the complexities
of status-bit redefinition?
No design has yet used a status-bit
to redefine completely the operation of
an opcode bit-pattern (as a “leading-
byte” does). However, the philosophic
difference between the Z-80 and the
2650 extends to the implementation of
their somewhat similar substitution of
one set of on-chip registers for another.
The Z-80 does this by a one-byte code
that exchanges the information between
its “on-line” set and its “off-line” one.
The 2650 uses a status-bit to “shift”
operation from one set to the other; this
makes use of the existing two-byte codes
for status-bit control, so it would seem
that lower code-efficiency is being
traded-off to save one new one-byte
opcode. However, the possibility exists of
simultaneously altering other control bits.
It’s hard to tell whether this would be
useful often enough to compensate for
the code-efficiency loss, or even how
often the alternation of banks of registers
will be used by programmers. Program¬
mers are the third group of cooks in this
cuisine, no less important than the
designers and executives who can decide
what the utensils shall be but not how
they’ll be used.
The register-interchange example
shows that a persistent state can be
established equally well by an opcode
byte as by a status bit. However it’s done,
the programmer has to keep track of
things. The 6809 has opcodes that cause
exchange between any pair of its regis¬
ters. As with the Z-80, the plethora of
possible codes allowed lots of new opera¬
tions !
The non-persistence of “leading-byte”
modification may seem to be an advan¬
tage inimitable by status-bit control, but
this is not so. A status-bit could be made
volatile or non-volatile by using a second
status-bit to control it. Consider the
6502 decimal-mode bit, and a hypotheti¬
cal new control-bit. A “set-both-bits”
code would be the equivalent of the
present, persistent SED, reversed only by
a “clear-both-bits” code. One-time
operation could be had by a “set-
decimal-clear-control” code; that would
cause an automatic clear of the decimal
bit by execution of any instruction
involving that bit, making it equivalent to
a “leading-byte” (except that it would
not have to precede immediately the
instruction code). Though not useful in
the arithmetic context, the principle
might work out well for status-bit
shifting of operations like 16-bit vs.
8-bit mode (for which the 6516 seems
to have created brand-new opcodes). Of
course, the same thing could be done
using two kinds of “leading-byte,” one
non-persistent (as now practiced) and the
other persistent until reversed. There is
some value in having a record of the
status in a register, for debugging use,
but the price entails having a second
status register. I rather like this, since any
otherwise unused bits could be used
(2650-style) for some kind of imaginative
application.
Although the two modes of opcode
redefinition could be made equivalent,
the status-bit mode has in fact only been
used to redefine a subset of the one-byte
opcodes that is expected to be used
repeatedly and exclusively in a subpro¬
gram. Persistence is desired, and the gain
is more in faster execution than in
economy of one-byte opcodes. The
“leading-byte” mode could not be
optimized in the Z-80 (because it
retained machine-code compatibility
with the 8080), but it is carefully crafted
in the 6809, that wisely sacrificed 6800
machine-code to gain efficiency. The
“leading-byte” in effect “calls in” a
new instruction set for a “one-time”
use. Since this is less code- and time-
efficient than the single-opcode-byte set,
the instructions in the two-byte-opcode
set are those expected to have a lower
usage frequency. This will be a self-
fulfilling expectation, since programmers
will avoid using them wherever possible!
The 6809 designers, well-aware that
programmers make the ultimate deci¬
sions, studied program usage of the 6800
set. This kind of systems analysis is no
doubt better than the inner-meditation
that must have played a major role in
the 6800 design. Yet, if the inner-
mediator is a creative genius he may
impose his will on programmers. I view
systems analysts as the contemporary
incarnations of the minor seers of the
past, and likewise fated to be auxiliaries
of the modern equivalent of kings. But
destiny sporadically spawns a major
prophet who can break into a truly new
world. What dinosaur, however skillfully
optimized, can withstand that?
The third generation of 8-bit micros
will have to be more prodigious than the
earlier ones. The 8080 had no competi¬
tion. Now it’s rife, and success will
require a quantum leap in performance,
not minor enhancement. I cannot even
hazard a guess as to how close we are to
the performance Emits of this level of
complexity!
Number 49 Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025 P a 9 e 23
374
a Multiple File
iflH
BY LAWRENCE E. HUGHES
Mycroft Labs, P.0. Box 6045
Tallahassee, FL 32301
Transfer Utility
ill
lllltc
This article describes the design and
use of a utility which makes it practical
to use a single disk drive on the Digital
Research CP/M operating system. The
entire source is included in this article,
and is also available from the author
on an 8" single density, 128-byte sector
diskette, along with a few other public
domain programs, from the above ad¬
dress, for $15. I hereby release MFT into
the public domain, for use on any CP/M
(or other) system. No right is granted
for resale, with or without modifications.
This program is the fifth generation
of a mechanism which can transfer files
from one diskette to another on a single
drive CP/M system. CP/M was originally
designed for use on a two-drive system,
and a reasonable mechanism was provided
for transferring files from one diskette
to another (PEP). Unfortunately, no
provisions were made for owners of one-
drive systems. A temporary kludge is
possible, which involves creating a “Pseudo
drive” B. With this DIOS extension,
anytime a new drive is accessed (via
SELDSK), the user is prompted to mount
the appropriate diskette in the one drive,
and hit CR when it is mounted. This is
simple enough to implement (if space is
available in the DIOS), and it allows use
of PIP to transfer files, but is somewhat
clumsy to use, especially with PIP, which
switches drives several times per file,
times per file.
Since it was fairly expensive for me to
upgrade my single drive Imsai FDC2-1
to a dual drive FDC2-1, I made several
attempts to solve the file transfer pro¬
blem, with increasing degrees of success.
Since I now have a dual drive Tarbell
system, and will probably not be making
any further improvements to MFT,
I have decided to release it into the public
domain. There are probably a number of
good folk out there who are currently
using a single drive system, or else are
holding off on disk altogether until they
can afford two drives—this program is
for you! Even owners of dual drive sys¬
tems may wish to study this code as an
example of a fairly elaborate utility which
interfaces to CP/M.
The following discussion is intended
to serve as a guideline to reading the
code, and was never meant to be parti¬
cularly useful without the accompanying
code.
Note the use of meaningful symbols
for the system interface addresses,
BDOS function codes, and FCB field
offsets. Note further that all I/O is done
via BDOS calls.
The first step is to clear the ‘break
flags’ (IBFLG and OBFLG). These will
be explained later. The next step is to
determine how much RAM is available
for use as a memory buffer. This is cal¬
culated by finding the starting address
of the BDOS (there is a pointer to it at
0006H), then subtracting from that the
starting address of the memory buffer
(which starts at the end of MFT). Note
that the buffer size is then rounded down
to the nearest multiple of 128 bytes.
The user is then notified of how large
the memory buffer is (in terms of 128
byte sectors).
At this point, the user is asked to
mount the input disk and type CR.
This allows the user to transfer files from
a disk which does not contain MFT.
Once a CR is typed, if IBFLG is set,
MFT jumps to MFT2A. IBFLG will
be set only if we left off reading a file
in the middle at the end of the last pass.
On the first pass, the routine CFNT
will be called to create the File Name
Table (FNT) from the list of ambiguous
file names on the command line. The
pointers IFNTP (pointer to the next file
to input) and OFNTP (pointer to the
next file to output) are reset to the
start of the FNT.
At MFT2A, the memory buffer point¬
er (MBUFP) is reset to the start of the
memory buffer (MBUF). MSIZE is set
to the total amount of available memory
in MBUF. If IBFLG is set, the rest of
the partially read file from last pass is
set up for reading where we left off.
Otherwise, the next available file from
the FNT is set up for reading, and the
file size (FSIZE) is set to 0.
At MFT6, the current file is read
into memory starting at MBUFP. As
each sector is read into memory, FSIZE
is incremented, MSIZE is decremented,
and MBUFP is advanced 128 bytes. If
MSIZE reaches 0, MBUF is full, hence
IBFLG is set, and reading ceases. If
either MBUF fills, or the end of the
current file is read, MFT8 is reached.
At MFT8, the current file is closed,
and the user is told how many sectors
were read into MBUF. Then the file
size (FSIZE) is stored in the FNT (along
Page 24
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
375
with the address at which this file started
in MBUF). IFNTP is updated to point to
the next file name to read. If IBFLG
is not set, there must still be room in
MBUF, so we loop back to MFT3 to
read another file.
At MFT9, we either have run out of
files, or MBUF is full, so we ask the user
to mount the output disk and type CR.
When the CR is typed, we make the new
disk Read/Write (via subroutine RESET).
If OBFLG is set, we are appending to the
end of a partially written file, hence we
reopen it where we left off. If OBFLG
is not set, we make a new file with the
name from the FNT which is pointed
to by OFNTP. Note that we force the
$R/W and $DIR attribute flags low for
2.0 users (can’t write to an R/O file).
We fetch the file size (into FSIZE)
from the FNT (at OFNTP). As each
sector is written, FSIZE is decremented
an MBUFP is advanced 128 bytes, until
FSIZE is 0. At this point, the file is
closed. We then tell the user how many
sectors were written, and loop to MFTA.
If the last file was only partially written
(IBFLG was set), then we set OBFLG.
When we finish the last file that was
read into MBUF, we jump to MFTF.
At this point, if IBFLG is set, we loop
to MFT1 and repeat this cycle until
all files in the FNT have been trans¬
ferred.
The subroutines are not described in
this article, since what they do is fairly ob¬
vious. Pay particular attention to GFN
and CFNT: all the others are trivial.
Note that a fair amount of error hand¬
ling is included at various points in MFT
to catch things like ‘No such files’,
‘disk full’, etc. Note also that as files
are transferred, the user is informed as
to what is going on. This is especially
important in a program such as this,
where the machine could be busy for
many minutes.
As far as style goes, note that the main
program comes first, followed by all
subroutines, then the messages, and final¬
ly by the RAM storage. The use of semi¬
colons to denote comments is consistent
throughout, and makes it easy to deter¬
mine where the different parts of the pro¬
gram lie.
For further information on the con¬
ventions of interfacing to CP/M, consult
the excellent Digital Research manual
set.
To use MFT, merely type its name,
followed by one or more ambiguous
file names (using ? and/or * wildcards).
You will be prompted to mount the input
disk and type CR. At this time the disk
with MFT may be removed, if the desired
files are on a different disk. Once the
input disk is mounted, the directory
will be searched and a list of all file names
which satisfy at least one of the ambi¬
guous file names will be compiled. As
many files as will fit into memory will
then be read. You will then be asked to
mount the output disk and type CR.
Note that MFT can write on this disk
without your having to ‘log it in’. All
data read from the input disk is then
written to the output disk. If more
files remain to be read, this cycle repeats
until all files are transferred. As an ex¬
ample, MFT *.* may be used to copy
all files from one disk to another.
Lawrence Hughes is a Computer
Research Specialist at Florida State
University by day, and runs My-
croft Labs by night. He works with
micro software in both pursuits.
He is the organizer and current
director of the Tallahassee Amateur
Computer Society, and past vice
president of the Atlanta Com¬
puter Society. He owns an Imsai
with 64K, dual 8” floppies, Heath
H-19, Decwriter, Hayes modem
and Hiplot plotter. His computer’s
name is Seymour and has the dis¬
tinction of being the first home
computer to be listed in the Atlanta
phone directory (under Computer,
Seymour T.).
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Number 49
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 25
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
377
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Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 29
379
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Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 31
381
A Cross Reference
Program
for Northstar BASIC
BY LARRY HUDSON
2232 Alameda Ave.
Ventura, Calif. 93003
Here is a combined line number and variable cross referenc¬
ing program for Northstar BASIC. Because this is a machine
language program, it runs much faster than the others I have
seen which were written in BASIC. This one will do a 500 line
program in about 30 seconds.
I have tried to write it to be as general as possible. All I/O
is through the normal Northstar DOS I/O, and naturally the
disk routines are through the DOS. All other subroutines are
within this program. The output routine uses the standard
Northstar convention of specifying the output device by the
code in the accumulator. As it is written now, it uses 0 for the
console device and 1 for a hard-copy device. These numbers
can easily be changed if needed.
It reads the program to be cross referenced directly from
disk. It accepts the standard Northstar convention of follow¬
ing the program name with the drive number. It creates the
cross references for both the line numbers and variables in the
same pass, and follows this with a second pass to flag any bad
line number references. After these lists are created, the pro¬
gram will ask which list you want printed, and when that is
done it will ask if you want another one. In the line number
cross reference list, any reference to a non-existent line is
flagged with an asterisk.
When answering the questions in the program, it will only
accept L or V for lines or variables, or Y or N for yes or no.
They can be entered in either upper or lower case, and no car¬
riage return is required. All other keys except Control-C are
ignored. The control-C will cause an immediate abort back to
the DOS. This is not the standard DOS control-C check; it will
not interrupt the running program; it is effective only when it
expects a keyboard input.
When entering the program name, either the underscore or
delete will backstep to delete characters. Both will echo the
underscore. This set of backstep characters can also easily be
changed. The buffer to hold the program name is only 11
bytes long, but the input routine keeps counters to prevent
overrunning either end of it.
This program loads in the area normally occupied by
BASIC, with the disk buffer located at address 2A00 through
2AFF. If you reassemble it for a different location, be sure
this buffer is located at a page boundary or the GETCHR rou¬
tine won’t work. There should be no other restrictions on loca¬
tions. The cross reference lists are created as linked lists im¬
mediately following this program.
2B00 is the normal entry point of this program. 2B03 is a
second entry point which jumps directly to the list printing
routine. Naturally, to be able to use this second entry point,
the lists must have already been created and must not have
been changed. However, this does make it possible to go back
to display or print more copies of the cross references without
reading the BASIC program again.
The data in addresses 2B06 and 2B07 are for the page
lengths of your console display and hard copy device. The
printing routine will pause after printing the specified number
of lines and wait for another keyboard input before continu¬
ing. This pause can be disabled for either of the output de¬
vices by storing a 0 as its page length data.
Each entry in the two main lists in this program, the VLIST
and LLIST, consists of three items. First is the link, which is
the memory address of the next entry. Second is the data,
either the variable or the line number with its good/bad flag.
Third is the first entry of another linked list of the line num¬
bers that refer to this data. Each entry in this set of lists, the
RLISTs, consists of two items, the link and the line number.
The last entry in each of the lists is marked by the link set to
zero. These relations are diagrammed in Figure 1. The program
keeps all these lists in order as they are created.
Finally, a few words about this assembly listing. This assem¬
bler allows a few extra non-standard mnemonics. The ones
used in this listing are:
CLA clear accumulator, assembles as XRA A.
SF set flags, assembles as ANA A.
SKP1 skip one byte, assembles as CPI without a data byte.
The DC pseudo op is for Define Characters. It assembles a
quoted string as a string of ASCII characters and it sets bit 7
of the last character high to serve as an end-of-message mark¬
er. The message display routines in this program are written to
use this format.
Page 32
382
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 33
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385
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
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390
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
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Solution oS Three First Order
Differential Equations with
an SR-52 Programmable Calculator
BY S. ANDREW YAKUSH PH.D.
Department of Biomathematics
School of Medicine
Loma Linda University
Loma Linda, CA 93250
Abstract
This paper presents a program
written for the Texas Instruments
SR-52 programmable calculator to
solve three first order ordinary
differential equations using a 4th
order Runga-Kutta method. Gener¬
al instructions for use of the pro¬
gram and a program listing are
given and a typical sample pro¬
blem done.
Introduction
In mathematical modeling and espe
cially the area of biological modeling,
effective models have been developed
using three first order ordinary dif¬
ferential equations of the form:
x' = f(t, x, y, z) x(t Q ) = x 0
y, = g(t,x, y, z) y(t 0 ) = y 0
z =h(t, x, y,z) z(t 0 ) = z 0
It is often helpful to be able to do some
preliminary examination of the model
before employing a computer to do the
major simulation. This paper presents a
program written for the Texas Instru¬
ments SR-52 programmable calculator to
solve this set of equations using a 4th
order Runga-Kutta method (7).
Program Description
The user is required to define the three
functions f, g and h using the labels
C, D and E. There are 61 program steps
(162-223) and 9 data registers (11-
19) available for user in defining the func¬
tions. For use in the functions f, g and
h the current values of x, y and z are
found in the registers R 02 , R03 and R o 4 •
The initial time t 0 is stored in register
Ro, and the initial states x 0 , y 0 and z 0
are stored in registers R 0 s,R06 an d R07
respectively. One half the integration
step size H/2 is stored in register R 9g
and the number of integration steps
is stored in register R 0 o •
The program is designed to use a PC
100 printer to print the values tj, x (tj),
y (tj) and z (tj) for i = 1.N where
tj = iH. If a printer is not available, pro¬
gram steps 147, 151, 155 and 159 can be
changed from PNT to HLT (see Table 2).
This will cause the program to halt
after each integration step and display the
appropriate values, then continue when
RUN is pressed. Each integration step
requires about 18 seconds in addition to
the time required to execute each of the
functions four times.
Table 1 contains the general instruc¬
tions for use of the program. Table 2 is
a listing of the general program.
Typical Sample Run
A model for the spread of an epidemic
and its control is described by the follow¬
ing equations(2):
S/= -cSI-v(t) S(0) = S G
I = cSI — rl 1(0) = I„
R' = rl R(0) = §
V ' - v(t) V(0) = 0
where S is the proportion of susceptibles
in the population, I is the proportion of
infectives, R is the proportion of recov¬
ered, V is the proportion who have been
vaccinated, c is the contact rate, r the
recovery rate and v(t) the vaccination
rate and S 0 + I 0 = 1. Since S +1 + R + V =
1, we need solve only the first three
equations, hence this program is ap¬
plicable. For the sake of simplicity we
will assume that v(t) is a constant.
Forty nine program steps were re¬
quired to define the three functions (see
Table 3). Table 4 shows excerpts of the
sample run which required a total of
about 6 minutes for execution which is
about 20 seconds per step. The para¬
meters chosen for this example are those
of the 6th case in Table 1 of (2).
Comments
The execution time for this program
is quite long even when compared to
a minicomputer. However, the conve¬
nience can often outweigh the slowness,
or make it possible to solve a problem
even when a computer is not available.
Another advantage is that the 12 digit
accuracy of the SR-52 is equivalent
to double precision on a 16 bit mini¬
computer. Since there are only 63 pro¬
gram steps available and 9 of these
are used for label definition and returns,
only relatively simple models can be
simulated. But as the sample shows,
there are meaningful models which fit
this criterion.
Programs to solve two first order equa¬
tions, a second order equation, or a third
order equation using the 4th order
Runge-Kutta method are available from
the author.
References
1. Bekey, G. A., and Karplus, W. J.,
“Hybrid Computation.” John Wiley
and Sons, New York, 1968.
2. Hethcote, H.W., and Waltman, P.
“Optimal Vaccination Schedules in a
Deterministic Epidemic Model,” Math.
Bios. 18, 365 (1973)
S. Andrew Yakush received the
A.B. degree from Andrews Uni¬
versity in 1966, the A.M. degree
from the University of Southern
California in 1972 and the Ph.D.
degree from the same institution in
1976.
Dr. Yakush joined the faculty
of the Biomathematics Department
in the School of Medicine of Loma
Linda University in 1972 where he
is an Assistant Professor and has
taught graduate courses in Bio¬
logical Control Systems and Bio¬
logical Modeling. He has also partic¬
ipated in several research projects
pertaining to the applications of
computers and mathematics to the
medical and biologcal world, and is
now project manager of the Image
Processing and Pattern Recognition
facility.
Page 44
392
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
Table 1.
General Instructions,
Table 3.
Sample Program
Step
Procedure
Enter Press Display
LOC
rn
KEY
LOC
Cl)
KF.Y
LOC
cn
KEY
LOC
CD
KEY
163
46
LBL
176
85
+
189
01
1
202
15
F
11 c
x’ - f(t,x,y,z)
164
13
C
177
42
STO
190
04
4
203
43
RCL
12 r
y’ = g(t,x,y,z)
165
43
RCL
178
01
1
191
75
-
204
01
1
13 v
z' * h(t,x,y,z)
166
01
1
179
04
4
192
43
RCL
205
02
2
14 cSI
167
01
1
180
43
RCL
193
01
1
206
65
X
l
Enter program CA t» B)
168
65
X
181
01
1
194
02
2
207
43
RCL
169
43
RCL
182
03
3
195
65
X
208
00
0
2
Enter f(Roi■ R 02> R 03' R 04)
into
C
CTO 163
170
00
0
183
95
.
196
43
RCL
209
03
3
R< r 01> r 02' r 03' r oD
Into
D
LRN
171
02
2
184
94
+/-
197
00
0
210
95
and h(Rgi,R o2> R 03' R 04)
into
E
.
172
65
X
185
56
RTN
198
03
3
211
56
RTN
.
173
43
RCL
186
46
LRL
199
95
-
.
174
00
0
187
14
n
200
56
RTN
LRN
175
03
3
188
43
RCL
201
46
LRL
3
Enter half integration step
H/2
STO 98
H/2
4
Enter number of steps
N
STO 00
N
5
Enter initial conditions
^o
STO 01
^o
x o
STO 05
x o
y 0
STO 06
Yo
z o
STO 07
z o
Printed
6
Start program
A
ti
X 1
Yi
z i
Available:
etc.
61 program steps (163-223)
9 data registers (11-19)
Table 2.
Program Listing.
LOC
CD
KEY
LOC
CD
KEY
LOC
CD
KEY
LOC
CD
KEY
LABELS
000
46
LRL
041
43
RCL
082
19
D'
123
09
9
A
Start
001
19
D'
042
00
0
083
44
SUM
124
17
B'
B
002
55
*
043
06
6
084
06
6
125
43
RCL
C
f(t ,x,y,z)
003
43
RCL
044
95
-
085
09
9
126
06
6
D
g(t ,x,y,z)
004
09
9
045
42
STO
086
56
RTN
127
0 7
7
E
h(t ,x,y,z)
005
09
9
046
00
0
087
46
LBL
128
44
SUM
A'
used
006
95
-
047
03
3
088
1 1
A
129
00
0
B'
used
007
55
RTN
048
43
RCL
089
25
CLR
130
05
5
C'
used
008
46
LBL
049
01
1
090
42
STO
131
4 3
RCL
D'
used
009
18
C'
050
00
0
091
00
0
132
06
6
E'
010
65
X
051
85
+
092
08
8
133
08
8
Oil
43
RCL
052
43
RCL
093
42
STO
134
44
SUM
012
09
9
053
00
0
094
00
0
135
00
0
REGISTERS
013
08
8
054
07
7
095
09
9
136
Oh
6
00
N
014
95
-
055
95
-
096
42
STO
137
43
RCL
01
ti
015
56
RTN
056
42
STO
097
01
1
138
06
6
02
xj+K/2
016
46
LBL
057
00
0
098
no
0
139
09
9
03
Yi+L/2
017
17
B'
058
04
4
099
03
3
140
44
SUM
04
zj+M/2
018
43
RCL
059
13
C
100
42
STO
141
00
0
05
x i
019
09
9
060
18
C'
101
09
9
142
07
7
06
Yi
020
08
8
061
4 2
STO
102
09
9
143
99
PAP
07
z i
021
44
SUM
062
00
0
103
16
A'
144
43
RCL
08
K/2
022
00
0
063
08
8
104
02
2
145
00
0
09
L/2
023
01
1
064
19
D'
105
22
INV
146
01
1
10
M/2
024
45
LBL
065
44
SUM
106
49
PRD
147
98
PNT(HLT)
025
16
A'
066
06
6
107
09
9
148
43
RCL
67
sum K/2
026
43
RCL
067
07
7
108
09
9
149
00
0
68
sum L/2
027
00
0
068
14
D
109
17
B'
150
05
5
69
sum M/2
028
08
8
069
18
C'
110
16
A'
151
98
PNT(HLT)
029
85
+
070
42
STO
111
02
2
152
43
RCL
98
H/2
030
43
RCL
071
00
0
112
49
PRD
153
no
0
99
3 or 1.5
031
00
0
072
09
9
113
00
0
154
06
6
032
05
5
073
19
D’
114
08
8
155
98
PNT(HLT)
033
95
-
074
44
SUM
115
49
PRD
156
43
RCL
034
42
STO
075
06
6
116
00
0
157
00
0
035
00
0
076
08
8
117
09
9
158
07
7
036
02
2
077
15
F.
118
49
PRD
159
98
PNT(HLT)
037
43
RCL
078
18
C'
119
01
1
160
58
DSZ
038
00
0
079
42
STO
120
00
0
161
11
A
039
09
9
080
01
1
121
49
PRD
162
81
HLT
040
85
+
081
00
0
122
09
9
Table 4.
Typical Sample Run.
Step
Procedure
Enter
Press
1
Enter program (A & B)
2
Enter definitions of f, g and h
CTO
163
(see Table 3.)
LRN
LRN
3
Enter model parameters
Contact rate c
10
STO
11
10.
Recovery rate r
6
STO
12
6.
Vaccination rate v
.4
STO
13
0.4
4
Enter initial conditions
0
STO
01
0 .
So
.99
STO
05
.99
.01
STO
06
.01
»o
0
STO
07
0 .
5
Enter integration paramaters
H/2
.05
STO
98
.05
N
10
STO
00
10.
Printed
6
Begin integration
A
0.1
S(.l)
.
9383331529
I <. 1)
.
0143969329
R(.l)
•
0072699143
t
0.5
SC.5)
6974981485
I(.5)
0
.034952619
R(.5)
•
0675492326
t
SO.)
0
1.
.402482465
id.)
.
0263862156
R<1.)
.
1711313194
7
Change vaccination rate
0
STO
13
0.
8
Enter additional steps
5
STO
00
5.
9
Resume integration
A
1.1
sd.n
.
3929749397
id.i)
.
0215503779
Rd.i)
1854746824
t
1.5
S(1.5)
3709168282
Id.5)
0089478071
Rd.5)
.
2201353647
Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 45
IMPROVEMENTS ON CP/M AND CDOS
Dear Suzanne,
Thank you for the great, all CP/M issue of DDJ #41.
I have a few comments to say regarding Jim Warner’s article
“CP/M and CDOS Program Compatibility.” There are two
small bugs involved with this program.
The first problem is that the function call 134 (FORMAT
STRING TO FILE CONTROL BLOCK) builds the FCB
correctly, but does not set the Next Record field to zero.
This means that when the file is read in, CP/M will begin read¬
ing at the Record Number of the last record read of the pre¬
vious file. This is normally only noticed under DEBUG when
reading in multiple files. The fix for this is simple, and only
adds 7 extra bytes:
NAM2:
CALL
DUMMY
;THIS IS PART OF OLD CODE
X0R
A
LD
(DE),A
;ZER0 FILE EXTENT
>
; THIS
IS THE
ADDED CODE
PUSH
HL
;SAVE HL REG PAIR
LD
HL, 20
;0FFSET FROM EXTENT TO NEXT REC.
ADD
HL, DE
;HL POINTS TO NEXT RECORD FIELD
LD
(HL) , A
;ZER0 NEXT RECORD
POP
HL
;RESTORE HL
; BACK
TO ORIGINAL CODE
POP
DE
RET
The second, very small, problem concerns another function
call. My version of EDIT (V00.10) does, as its first function
call a GET VERSION AND RELEASE NUMBERS (8DH).
As far as I can tell, EDIT does not care what values come back
as the version and release numbers. There are two possible
solutions to this.
1. Patch EDIT to eliminate the call.
The offending code (for EDIT V00. 10) is at location
021CH. The original code is
021C LD C.8DH
021E JP 5
If location 021CH is changed to a ‘RET’ instruction (C9)
this eliminates the function call, and EDIT appears to operate
correctly.
2. Change FILTER to ignore any undecoded function calls.
This may seem to be drastic, but I can report no problems
with it in my experience. Change the instruction in FILTER
Apart from these two small problems, I found Mr. Warren’s
article both enjoyable and very useful, and so I thank both
him and you for it. Keep up the good work.
Sincerely, 25 Buena Vista Drive.
Leigh F. Fiddes Montmorency. 3094.
AUSTRALIA.
MORE ON INDIRECT ADDRESSING
FOR 8080/Z80
Dear DDJ :
With reference to “Indirect addressing for the 8080 and
Z80” (DDJ #47), an alternative way to implement LHLI is
; LHLI performs HL:=(HL)
LHLI: PUSH PSW
MOV A,M
I NX H
MOV H,M
MOV L,A
POP PSW
RET
This is more efficient than the “miniprogram” technique
described and avoids the gaucherie of self-modifying code.
Similarly,
; IXMOV performs A:=(A+X)
IXM 0 V: PUSH 0
PUSH H
PUSH X
POP H
MVI 0,0
MOV E,A
DAD D
MOV A,M
POP H
POP D
RET
Obviously, macro versions of this could be written to
handle indexed moves to other registers. Also, the PUSH-
POP pairs may be omitted when the application does not need
the corresponding registers saved.
JP NZ.IGOR ;NOT DECODED, ** ERROR ** Sincerely,
to David Ecklein
RET NZ ;NOT DECODED, IGNORE AND RETURN
Tesseract Associates
Stinson Lake Road
Rumney, New Hampshire 03266
Page 46
394
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
INTERFACING H -14 TO HORIZON
ADDENDUM TO “ZX65”
Dear Editor:
May I make the following suggestion in response to John
R. Dye, {DDJ #47), regarding interfacing a Heathkit printer
H- 14 to a North Star Horizon.
Instead of trading away a very nice printer, why not make
it run full speed? The North Star Horizon ports are extremely
flexible and can interface to almost anything. You may wish
to publish the following 3-wire configuration setup to assist
others who wish to wed these two devices.
On the Motherboard header at location 4D, solder a wire
from pin 7 to pin 8 and also a wire from pin 9 to pin 10.
Then solder a wire from pin 12 of header 4D over to pin
12 of the header at location 2C. These 3 connections should
be the only ones on these headers.
This allows the printer to run at full speed by having the
printer’s buffer full signal (interface pin 15) drop Clear to
Send to the second serial port USART. No software changes
are necessary.
Sincerely, 3417 Hickory Hills Drive
Warren B. Saunders Oakton, Virginia 22124
Dear Editor:
I am writing in reference to J. R. Dye’s letter in DDJ
#47. I agree with him that you should be aware of the com¬
plexity of integrating different manufacturers’ hardware.
Mainframe manufacturers’ suggested configurations in many
cases do not represent the best alternative to a user’s needs.
There is no substitute for knowledge of your hardware’s
capabilities. The North Star Horizon has the needed hardware
and software to perform the simple handshaking the H14
printer requires. I’ve successfully interfaced a Texas Instru¬
ment’s 810 printer to the Horizon’s serial ports.
This printer buffers incoming data until whole lines have
been received. The printer then prints the buffer while holding
pin 20 of the EIA interface low (DNB option in the 810
printer must be selected). The serial output routine must be
able to detect this low signal and hold further output as the
printer logic is BUSY printing the buffer.
The STANDARD serial output routine in the NORTH
STAR DOS tests the least significant bit (TxRdy) of the serial
port status byte. This bit is ON if the serial port is ready to
receive a character from the CPU for output processing. This
bit is affected by the CTS (clear to send) input to the 8251
USARTs that control the serial ports. The CTS input is termi¬
nated at pin 12 of the serial port config header.
In my application it was a simple matter to rewire the
serial config header to jump (EIA pin 20/header pin 1) to
(header pin 12/8251 input CTS). This turns OFF TxRdy bit
in the serial port status byte when the busy printer is holding
EIA pin 20 low. Note that a low on header pin 12 results in
a high at the 8251 due to inverting EIA receiver.
Be aware that more is involved than just the above details
in making the interface work. You must carefully scrutinize
hardware documents in building the config. header and I/O
cable. Your objective should be to get a low signal to pin 12
of the serial config. header signifying the printer is busy.
Pitfalls such as inverting EIA receivers/drivers, strapable
hardware options and special I/O cables can make a maze
out of the best documentation. I have personally experienced
the excellence of North Star’s hardware manual as well as the
T.I. 810’s. I would suggest you find a more knowledgable
Horizon dealer, friendly or not.
Sincerely, 2021 N. 22nd Street
John T. McCarron Phoenix, Arizona 85006
Dear Editor:
A potentially serious error in “ZX65: Simulating a Micro”
(DDJ #47) has been pointed out to me by a user. It is sys¬
tem dependent and, fortunately, fairly rare. In those cases
where the problem exists, however, ZX65 simply won’t accept
input from the console keyboard, and thus will not respond to
commands once loaded.
The problem is that ZX65 expects the user’s console print
routine CONOUT to return with the character just printed
still in the accumulator. In those few instances where this
doesn’t happen, the following patch will solve the problem:
ADDRESS
OBJ CODE
INSTRUCTION
7A28
C3 80 7D
JP 7D80
7D80
F5
PUSH AF
7D81
CD 0C 7E
CALL CONOUT
7D84
FI
POP AF
7D85
C9
RET
This patch can be inserted by loading ZX65.COM under DDT,
making the changes using the “S” function, and storing the
modified code back to disk, following warm start, by typing
“SAVE 15 ZX65.COM”
Respectfully, 6221 Woodlow
Richard M. Kruse Wichita, KS 67220
WHEN MINIMUM VALUE EQUALS MAXIMUM
COST
DDJ:
Most readers probably feel, as I do, that the goal of all
human enterprise is to provide maximum value and service
at minimum cost. This minimum can never be zero, since
someone must pay the piper. I was therefore interested to
learn that someone at Prentice-Hall did not agree that the
numerical value of price is always positive. They sent me,
earlier this year, no less than two announcements of a new
book, Microcomputer Interfacing, by Bruce Artwick. Each had
a postcard saying: “Yes, please send me a FREE 15-day exam¬
ination copy. After I’ve seen (it) . . .I’ll send you my check for
$18.95 plus postage and handling. Otherwise, I’ll return the
book during the 15-day trial period and owe nothing.” My
normal tactic for new books is to wait until they show up in a
bookstore, and to look them over very carefully before arri¬
ving at a decision (usually negative, since truly fine books are
rare). So I ignored the first P-H message, but when the book
failed to appear I sent in the second postcard. So that my tiny
circle of admirers will not feel that I have lapsed into senility,
let me add how I interpreted the word FREE as used by P-H.
Since the retail markup of a book is 40-50%, I assumed that
P-H was not really expecting to reap this for itself, but wished
to provide extraordinarily early availability—a special serv¬
ice-while absorbing the extra costs (trivial handling charge,
etc.).
The P-H interpretation of the word FREE is significantly
different. I had sent the card in May. Nothing happened.
In late June, the book appeared in a local bookstore. A very
small book, technically OK, not worth the price ($20.18,
including sales tax.) My examination of it was really FREE
for me, though of course the principle that nothing is free
Number 49
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Page 47
395
was not violated —the overhead costs to the store are ulti¬
mately paid, by me and others, as part of the price of the
books we buy. That’s fairness.
Yesterday, the P-H computer acknowledged my card of
last May by sending me a bill for $23.09, itemizing the base
price plus $2.73 postage and handling, plus $1.41 sales tax.
This tax is 18 cents higher than the local tax, since the com¬
puter is programmed to tax the postage-and-handling too.
The computer also knows that the Berkeley tax is 6.5%,
not 6% as in most of the state. It doesn’t know that the card
it was answering forgot to mention a tax, or that there is as
yet no book. It is probably now counting down from 15 days,
when it will emit a second bill. As to the book itself, the mills
of the gods (notoriously slow) may even now be grinding away
at this trivial problem. For the scam to be truly perfect, it
ought to appear on day — 1 of the countdown! The FREE
offer would then become an unconditional sale, delivered
4+ weeks later than I could have got it in Berkeley and at a
price $2.91 higher. This idiotic rigmarole perhaps makes
sense for a potential buyer in the middle of the Sahara desert.
The P-H computer, so deeply versed in the minutiae of taxa¬
tion, is unaware that Berkeley is awash with books.
Fairness compels me to acknowledge that the P-H organiza¬
tion is not made up 100% of nitwits (except perhaps at its
selling end). Last May I had a phone call from the Bay Area
P-H representative, Howard Welt, an intelligent and courteous
man. He had seen my articles on Instruction Sets in Kilobaud
Microcomputing , and wondered whether I had enough
material for a book. I said no, explained why not, and sug¬
gested names of people who might be interested. Later, I wrote
him a letter with supplementary information. No “handling
charge” (P-H) since I’m a true believer in the dissemination of
information at minimum cost. That’s the major role of a
university. I don’t expect book publishers to operate at a loss.
Still, they also are disseminators of information. I do expect a
high level of integrity and efficiency. The cost of the Artwick
book could have been reduced by using paperback instead of
hardcover. Since such books begin to obsolesce before the ink
is dry, softcover makes better sense.
Sincerely, College of Natural Resources
Hal Gordon University of California
Berkeley, CA 94720
TOO MUCH Z80, 8080 AND CP/M
Dear Dr. Dobb’s:
Thank you for the issue on the Language C (DDJ #45). It
is nice to see some recognition for alternatives to PASCAL.
Tim Pugh’s article in DDJ #46 on MCALL-C, while inter¬
esting, contains an instance of the much-too-prevalent atti¬
tude that everybody who has a disk system is using it with a
Z-80 or 8080 and is running CP/M. For a column and a half,
the article, which is about a communications protocol for
sending files from one personal computer to another, could
apply to any computer with a modem and a disk. Then he
answers the question of why it takes an indeterminate amount
of time to open a file by saying that it’s because of the wide
variety of disks and controllers that can be used with CP/M!
I was expecting something more like: it’s because of the wide
variety of disks, controllers, operating systems, and processors
that are in use. Instead, we are apparently intended to assume
that the only disk operating system (DOS) that exists is CP/M
(and by implication, that the only microprocessors that exist
are the 8080 and Z-80). To be fair to Mr. Pugh, he has deve¬
loped the protocol on a CP/M system and is apparently selling
this CP/M implementation of it. However, there is nothing
about the protocol that requires CP/M. It could be imple¬
mented for any DOS on any processor.
I would like to clarify the remarks I made in my letter that
appeared in DDJ #46 (page 55). My statement that CP/M
will not be “universal” until there are versions of it for many
other processors (6800, 6502, etc.) was not intended to imply
that I advocate such implementations. CP/M has a number of
limitations and shortcomings that should not be perpetuated
in other operating systems. The biggest such problem is
probably the lack of device-independent I/O, as well as the
fixed and rather limited number of devices supported. CP/M
keeps track of the size of disk files in sectors rather than in
bytes. Thus, a special data character (control-Z) is required to
mark the end of a text file, and files containing “binary” in¬
formation must be a multiple of 128 bytes in length. These
features, resulting to some degree in two file types or formats,
are at best unattractive. The orientation toward disks with
128-byte sectors, toward terminals with upper case only,
its encouragement of assembly language for almost all pro¬
gramming; the restriction, removed in the latest release, to
disks of 256K bytes or less; the rather clumsy method of
random access to disk files, improved in the latest release;
and the fact that processing and I/O cannot be overlapped are
also problem areas. Perhaps it is because of some of CP/M’s
limitations that it can run on as many different systems as
it does.
Sincerely, 5472 Playa Del Rey
Jim Howell San Jose, CA 95123
Page 48
396
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia, Box E, Menlo Park, CA 94025
Number 49
© David Dameron 1979
397
Dr. DoBB'S JoURNALof
COMPUTER
(Calisthenics ^Orthodontia
Running Light Without Overbyte
Number 50 November/December 1980 Volume 5, Issue 10
A REFERENCE JOURNAL FOR USERS OF HOME COMPUTERS
N-Logs: A New Number Language for Scientific Computers 4
Keneth A. Simons
Las Vegas Super Slot: A CP/M Game Machine Program Using Flashwriter I Graphics 10
David W. Freidman
Quick-Key: A North Star BASIC Statement Generator 23
Leonard E. Garcia
TUTOR: A Foreign Language Vocabulary TVainer 29
Gary D. Gaugler
Interfacing the WH14 Printer to Your Microcomputer’s Serial Port Is Simpler Than You Think 30
Lachman Sippy
and more ...
399
\IO(.S
ANEW
NUMBER LANGUAGE
FOR
SCIENTIFIC COMPUTERS
by Keneth A. Simons
SUMMARY: The N-log is so defined that it is a simple
positive integer used to represent any number, with any re¬
quired precision. No suffixes, prefixes, exponents or decimal
points are needed to allow symbolizing the entire range of
numbers encountered in scientific computations. N-logs
are particularly useful with digital computers, eliminating
the need for floating point routines and exponential notation.
A procedure is described that allows finding the N-log of
the sum or difference of two numbers, when the N-log of
each is known, without converting from N-logs to numbers or
vice-versa.
INTRODUCTION: Since men first started numbering and
measuring, the results have been written symbolically. There
is, for example, not the remotest relationship beween the
symbol ‘2’, or the word ‘two’, and a pair of things as they exist
in nature. We have all become accustomed to the fact that one
represents the other, but the whole idea is strictly man¬
made. Since this is true, it is perfectly allowable to look for
other, and possibly more convenient, ways of representing
numbers. A good example is found in the hexadecimal system
where, because it is convenient in the computer context, we
use, for example, the symbol A to represent the number that
has been symbolized by 10 for at least a thousand years!
This paper describes a new way of representing numbers which
is based on simple fundamental principles and has many
advantages over conventional methods.
THE DEVELOPMENT OF SYMBOLS FOR NUMBERS:
When a prehistoric farmer asked his slave how many hogs were
Keneth A. Simons —2035 Willowbrook Drive, Huntingdon
Valley, PA 19006
in a field, the man might have held up nine fingers, or made
nine scratches in the dirt, like this:
This system was direct, but became cumbersome for the
wealthy with lots of pigs! So a better system evolved wherein
one counted four pigs, then scratched diagonally across to
show the fifth. With these symbols twenty-four pigs would
appear as:
One simply counted up how many fives there were, added
the odd ones and arrived at the number.
ROMAN NUMERALS: As history progressed it became
necessary to deal with larger numbers, and a simpler system
was needed. The Romans came up with a scheme where letter
symbols were used for numbers. Thus I represented one, V
was used for five, X for ten, L for fifty, C for a hundred, and
so on. Any number could be portrayed by writing the appro¬
priate symbols in a row, with the smaller ones on the right.
The number represented was understood to be the sum of
the numbers indicated by the symbols. Thus CCLXI meant
two hundreds (CC) plus a fifty (L) plus a ten (X) plus one (I),
or two hundred and sixty-one. Unfortunately, at about this
time, mankind became interested in calculation. With the rise
of commerce and the early beginnings of the sciences it be¬
came necessary not only to be able to write numbers but also
to use them in calculations. The processes of multiplication,
Page 4
400
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
division and the expression of fractions were extremely clumsy
using the Roman system. As Dr. Jacob Shekel once said,
referring to the failure of the Romans to recognize the use¬
fulness of a symbol for zero, “Their trouble with numbers
was that they didn’t know nothing.”
ARABIC NUMERALS: Fortunately a system had been in
use in the Arabian countries for centuries based on three
revolutionary and incredibly useful concepts. This system was
to be adopted by the Western world, and it played an import¬
ant part in making possible the rapid development of the
physical sciences during and after the Renaissance. These
concepts were:
1. Nothing was given a name (zero) and a symbol (0).
2. The next nine numbers were given both names and symbols
with the English names: one (1), two (2), three (3), four
(4), five (5), six (6), seven (7), eight (8), and nine (9).
3. The weight of a given digit was indicated by its position.
Thus the right-most digit was assumed to be multiplied by
1, the next digit to the left by 10, the next by 100, and so
on.
Using the Arabian system the symbol 9870 would be inter¬
preted as (9 X 1000) + (8 X 100) + (7 X 10) + (0 X 1). This
way of symbolizing numbers greatly simplified the algorithms
for the needed mathematical calculations so that, compared
with earlier systems, these calculations were accomplished
much more rapidly.
FRACTIONS: With the acceptance of Arabic numerals, an
additional need developed —the need to represent numbers less
than one. Unfortunately a solution arose which originated
centuries of confusion from which we still suffer: the fraction
was introduced! Numbers less than one were represented as
the quotient of one integer divided by another. These symbols
were clumsy to write, and, as any grade school graduate
knows, calculations involving them were complex and cumber¬
some. To make matters worse the British embraced the idea
and saddled us with a system of measurement that is incredi¬
bly inefficient. They did, in retrospect, the strangest things,
avoiding the number 10, the base of their number system, as if
it were a plague! A mile was divided by 1760 (where did that
come from?) to get the yard. The yard was divided by 3 to get
the foot (why 3 rather than 5 or 10?) The foot was split into
12 parts (they couldn’t use 10, it might simplify things) to
get the inch. Then they ran out of names, so smaller sizes were
expressed as fractional parts of an inch, right on down to
l/64s. The whole mess has become part of our culture, and
probably has wasted more man-hours of intellectual effort
than all of the World Wars combined!
DECIMAL FRACTIONS: A much simpler way of represen¬
ting numbers less than one followed the invention of the
decimal point, and the discovery that a self-consistent system
resulted when the first digit to the right of that point was
assumed to be divided by 10, the second by 100, the third by
1000, and so on. With this approach the symbol .235 represen¬
ted the sum of 2/10 + 3/100 + 5/1000. The great advantage
of presenting numbers this way lay in the fact that all of the
calculating algorithms that worked with integers were equally
useful with numbers containing decimal fractions, as long as
care was used to place the decimal point in the right position
in the result. They had the further advantage that they were
easier to write since there were no numbers above or below the
line. Decimal fractions are almost universally used in today’s
pocket calculators, which generally don’t display ordinary
fractions It seems possible that, between these calculators and
the almost world-wide adoption of the metric system, the
world may (except for some back-water areas like our own
country!) at long last get rid of the English system and the
ordinary fraction.
EXPONENTS AND EXPONENTIAL NUMBERS: With
the rapid development of astronomy, physics and the other
natural sciences in the 16th and 17th centuries, came the need
for improved ways of handling very large and very small
numbers. Astronomical measurements showed, for example,
that the distances to even the nearer stars were so great that
they could conveniently be expressed by using a ‘light year,’
the distance travelled by light in one year. One light year is
about 6000000000000 miles. In physics it was found that the
rest mass of an electron is something like 0.000000000000000
0000000000000001 kilograms. It was obvious that it was
impractical to express numbers like this with ordinary
numerical notation. A more compact and convenient numeri-
ca language was needed.
It had been customary for some time to express the number
of times a number is multiplied by itself by the use of an
‘exponent,’ a tittle numeral written above and to the right.
Thus 2 times itself, called “two squared,” was written 2 2 .
2X2X2, called 2 cubed, was written 2 3 , and so on. The
use of the number 10 with various exponents turned out to be
a very effective answer to the problem stated above. Since
10 12 = 1 followed by 12 zeroes, an awkward numeral like
6000000000000 could be broken up into the product of 6
by 1000000000000, written simply as 6 X 10 12 . This tech¬
nique provided a much simpler and more satisfactory way
of dealing with very large numbers. To deal with small num¬
bers the fact was used that a number with a negative ex¬
ponent is equal to the inverse of the same number with the
same exponent having a positive sign. Thus 10 -4 = 1/10 4
= 0.0001. The rest mass of the electron, written above with
30 zeroes followed by a 1, could be expressed much more
compactly as 1 X 10' 31 kilograms. Numbers expressed in this
way, i.e., using an exponent, are called “exponential numbers”
and this technique for handling very large or very small num¬
bers is called “scientific notation.” It is used almost universally
in scientific work where large or small numbers are involved,
and is available in most calculators and computer languages
intended for use by those concerned with scientific calcula¬
tions.
LOGARITHMS: Another important numerical language
that is closely related to the exponent is the logarithm. The
basis for logarithms is the fact that any number can be raised
not only to a power which is an integer (e.g. 8 6 =262144 or
3 4 =81). but also to a power that includes a decimal fraction
(e.g. 2*' 89 = approximately 3.706, 10 1-1 = approximately
12.59). The logarithm of any number is simply the power to
which some other number (called the “base”) must be raised
to equal it. Thus, referring to the examples above, the loga¬
rithm of 262144 to the base 8 is seen to be 6 (since this is the
power to which 8 must be raised to equal 262144); and the
logarithm of 12.59 to the base 10 must equal 1.1 for the same
reason.
Logarithms were originally discovered by Napier, who used
the number “e” (=2.71828. . .) as his base. His reason for this
choice was that the logarithm of a number to this base (called
its “natural” logarithm) is relatively easy to compute. This is
also the reason why many computer languages give the natural
logarithm. Briggs later discovered that, since our numerical lan¬
guage, the decimal system, is based on the number 10, 10 also
makes a very convenient base for logarithms. He, and others
who followed him, compiled tables of these logarithms which
formed, for almost 250 years, the basis for almost all accurate
computations in the sciences and in surveying.
The advent of the electronic computer in the middle of the
20th century changed all that. Its speed and facility are so
much superior to that achieved with logarithms that the use of
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 5
401
the latter for computation has practically crushed. In the
1961 edition of the Encyclopedia Brittamca VKet. 1) h.. VJ.
May states that . . logarithms (are) virtually obsolete for
large-scale computation, though they are used in the 1960’s
for a few special purposes and indirectly as the basis of the
slide rule.” (In 1980 even this use has disappeared, although
the logarithm still remains as the basis for the decibel, widely
used in communications and acoustics.)
It is a strange quirk of history that today, when the compu¬
tation of a logarithm requires only the operation of an inex¬
pensive pocket calculator, the need for them has almost com¬
pletely disappeared! Almost all the computations that former¬
ly required logarithms are now done by these same calculators,
or their big brothers, the electronic computers. The object of
this paper is to propose a new idea, inspired by the almost uni¬
versal acceptance of the decibel. What is proposed is the use of
the logarithm as the basis for a new numerical language, called
“N-logs” which, being integers, are more convenient for
people to handle, and especially suited for use as input and
output numbers for computers.
PRECISION AND ACCURACY: Since one of the major
advantages of N-logs has to do with their precision, it is im¬
portant to establish clearly what that word means. The Inter¬
national Dictionary of Applied Mathematics (Ref. 2) defines
“accuracy”:
Accuracy: The degree of exactness actually possessed by an
approximation, measurement, etc. It may be contrasted with
precision which is the degree of exactness with which a quanti¬
ty is expressed. For example, as a value for Tt the number
3.1428 is more precise than accurate.
This is, of course, because that number is in error by about
.04% (as compared with the correct value, 3.1416), whereas it
is stated with a precision of plus or minus 0.0016% (the
maximum range of numbers implied by the digits 3.1428). As
another example, suppose that a digital voltmeter reads
8.19271 when measuring a certain voltage, but it had been cal¬
ibrated against a voltage standard which had an error of 0.1%.
The accuracy of this measurement, limited by the standard,
would be only 0.1%, while the precision of the reading would
be about 1 part per million, 1000 times better.
THE PRECISION OF RATIONAL NUMBERS: All of the
numbers that report the results of measurement in engineer¬
ing and the sciences are “rational numbers” since they must be
written with a limited number of digits, and, for the same
reason almost all of them represent approximations (the single
exception being integers that result from counting a few
items, which are the only numbers we deal with that can be
exact). Because of this it is important to ask what factors af¬
fect the precision of numbers as they are usually written. It is
common to speak of “three figure accuracy,” implying that
the precision is affected only by the number of digits. Unfor¬
tunately this is not true. The precision with which a number is
written depends not only on the number of digits that are
used, but on what those digits are. As an example the number
9821, as an approximation, represents the result of rounding
any number between the limits 9820.5 and 9821.5. With four
significant figures, the number has a precision of 51 PPM (the
error of 9821.5 compared with 9821). The number 1032, on
the other hand, with the same number of digits, is written with
a precision of only 484 PPM (the error of 1032.5 compared
with 1032), almost 10 times poorer than 9821! This problem
of variable precision is inherent in our number system, and is
a result of the fact that it was developed for counting, rather
than for measuring ratios, so that each successive number in a
series, as we write it, is arrived at by adding a fixed small num¬
ber to the previous one.
Page 6
402
THE PRECISION OP LOGARITHMS: By contrast consist
the LOGs (see -NOTE, p. 36) ot the two numbers written above.
The LOG of 9821, written with three digits to the right of the
decimal point, is 3.992. Since this number approximates all
LOGs between 3.9915 and 3.9925, it represents all numbers
between 9806 (EXP 3.9915) and 9829 (EXP 3.9925) and it
represents these numbers with a precision of about 0.12%.
Compare this with the LOG of 1032, which is 3.014. This re¬
presents the spread of numbers between about 1032 (EXP
3.0135) and 1034 (EXP 3.0145), also showing a precision of
about 0.12%. This illustrates a fact that is basic to this pre¬
sentation: the precision with which a LOG represents a num¬
ber is determined only by the number of digits in the LOG to
the right of the decimal point, and is not affected by what
those digits are. It is for this reason that logs are called “the
language of ratios,” and make an excellent numerical language
for reporting ratio measurements.
PEOPLE PREFER INTEGERS: Most people dislike frac¬
tions (including the decimal kind) and avoid using them when¬
ever possible. A person who goes into a lumber yard asks for a
“2 by 4,” although the actual dimensions of the board he
wants are close to 1-3/4 by 3-3/4 inches. He asks for “Num¬
ber 22” wire at the radio store, when the actual diameter of
the wire he wants is around 0.025 inches. Although he actually
pays 0.17 times the principle on his mortgage, he calls this
“17%.” The whole complicated series of prefixes for metric
measurements is chiefly aimed at keeping the numbers used as
close to integers as possible. We’d much rather say 83 milli¬
meters than “0.083 meters;” 102 microhenries is less of a
mouthful than 0.000102 henries. One rather silly place where
this breaks down is in the measurement of capacitors. Through
long-standing custom we almost always say “.005 micro¬
farads” rather than “5 nanofarads,” which is just as correct
and much easier to state.
THE DECIBEL: One of the cleverest dodges for turning
complicated numbers into integers was invented at Bell Labor¬
atories in 1924. They multiplied the LOG of any power ratio
by 10 and obtained a beautifully simple series of integers to
describe the quantities which most concerned them: gain, loss
and power levels in telephone systems. Unfortunately they
made two mistakes that severely limited the spread of their
idea. In the first place they insisted that the process could only
be used with power and power ratios (which limitation has no
basis in fact since, obviously, the LOG of any number can be
taken, and the result multiplied by 10, whether the number re¬
presents power, resistance, length or the population of Malay¬
sia!) (see Ref. 3) The only sensible question is “Does this pro¬
cess yield a convenient result?” If it does, it should be used.
The other mistake the Bell people made was to adopt a very
confusing terminology. They said, for example, that the atten¬
uation of a section of telephone line was measured and ex¬
pressed in terms of a unit, the decibel. They considered atten¬
uation as a measurable Physical Quantity (which it is, being a
measurable property of a Physical System), but they also con¬
sidered the dB as the Physical Unit in terms of which this
quantity was measured. One dB is no more a Physical Unit
than the number 3! The statement “The ratio is one decibel”
means nothing more nor less than “10 times the LOG of the
ratio = 1,” i.e., the LOG of the ratio is 0.1 and, since EXP 0.1
- 1.259, the ratio is approximately 1.259. The number 1.259
can, by no stretch of the imagination, be called a unit of any¬
thing!
N-LOGS-EXPRESSING ANY NUMBER AS AN INTE¬
GER: Since it is clear that people prefer integers, it makes
good sense to look for a number language that allows expres¬
sion of any number in that form. The decibel approach points
the way, 10 times the LOG of any number can be rounded to
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
form an integer but when this is done the precision of the
expression is restricted. This can be seen if we consider the
range of numbers represented by, for example, 3 decibels. The
corresponding nominal ratio is found from 10 X LOG X = 3,
LOG X = .3 and X = EXP .3, i.e., X = 1.995. At the upper lim¬
it 10 X LOG Y = 3.5, and Y = EXP .35 = 2.239. Since 2.239 is
12% higher than 1.995, and LOGs with the same number of
significant figures to the right of the decimal point represent
the corresponding number with the same precision, it follows
that dBs, rounded to integers, have a basic precision of plus or
minus 12%. Since this precision is inadequate for many appli¬
cations, the next question is “How can the precision be im¬
proved without losing the important advantage of the integer
presentation?” The answer is very simple. As with any other
decimal number, multiplying a LOG by 10 has the effect of
moving the decimal point one place to the right. Thus 3 dB
is simply the LOG .3, with the decimal point shifted. To move
that point two places would require multiplication by 100,
three places would require 1000, and in general, to move the
decimal point in a LOG “N” places requires multiplying the
LOG by EXP N, where N is 1, 2, 3, 4, 5, 6 and so on, as
required. From this follows the definition of N-logs:
The N-log of a number is that integer most closely ap¬
proximating the product of EXP N and the LOG of the
number.
It should be noted that N is not necessarily an integer. In fact
the multiplier, defined above as 10 N , can be any number. The
implications of this fact are very broad, showing that one has a
wide choice of multipliers so that the use of the N-log con¬
cept is not restricted to the decimal system, but can be used
with any number language. However our calculators and our
brains are both more at home with the 10-based system, so
the general case will not be explored further in this paper.
Since N-logs as defined above, where N is a small integer,
are easily found with a pocket calculator, it makes sense to use
them. An understanding of the characteristics of each “fami¬
ly” (i.e., the N-logs resulting from each choice of N)is essen¬
tial if the idea is to be applied to practical situations. Table I
shows how the choice of N determines the number of digits in
the N-log, and the precision with which it can express a
number. It can be seen that these families provide a very wide
range of capabilities.
TABLE I
The Properties of the First Seven Families of N-logs
Faitily
N
Multiplier
It of Digits*
Precision
1-Logs
t
10
3
♦
12
z
2-Logs
2
100
4
♦
1.2
z
3-Logs
3
1,000
5
+
0.11
z
4-Logs
4
10,000
6
♦
0.011
z
5-Logs
3
100,000
7
+
11
PPM
6-Logs
6
1,000,000
8
+
1.1
PPM
7-Logs
7
10,000,000
9
♦
0.11
PPM
* The number of digits is that required to represent numbers
between 10”" and 10 + ".
N-LOGS SIMPLIFY EXPRESSIONS: The simplicity
achieved by the use of N-logs can best be illustrated by a few
examples: The mean distance from earth to the sun is
9.3 X 10 7 miles. The Two-log of this distance in miles is 797,
expressed with a precision of ± 1.2%. Instead of reporting the
result of measuring a certain capacitor as “986 picofarads” it
could be expressed by stating the Three-log of the capacitance
in farads, which is -9006, with a precision of ±0.11%. One
light year, stated as the Six-log of the number of miles, is
12768973, expressed with a precision of about 1 PPM. The
rest mass of the electron, in kilograms, is expressed, including
the accuracy with which it is known, by the Six-log -30040-
502±6. Since a change of 1 in the right-hand digit of a Six-log
corresponds to about 1PPM (regardless of what the digits are)
this states, without the use of any additional symbolism (like
PPM or %), that this quantity is known with an accuracy corre¬
sponding to ±6 PPM. This simplicity in the statement of toler¬
ance is one of the several advantages of N-logs.
AN N-LOG IS SIMPLY A LOGARITHM TO A DIFFER¬
ENT BASE : The bases that have been used for systems of loga¬
rithms in the past have been a small group. They include
10 as the base for Common Logarithms; the number “e”
(2.71828 .. .) as the base for Natural Logarithms; and more re¬
cently 2 as the base for logarithms relating to computer opera¬
tion. This paper is an attempt to show that many other bases
are not only possible, but sometimes very convenient. To show
that an N-log, as defined above, is simply a logarithm to a
base which is different from 10, e or 2, some new terms are
needed. In what follows the word “log” will be used to mean
a logarithm in general, i.e., one taken to any base. With a sub¬
script (“log x ”) it will indicate a logarithm to the base indi¬
cated by the subscript, e.g., log 2 will mean the logarithm to
the base 2.
The formula for changing the base of a logarithm can be
found in any elementary Algebra text. One way to state it is:
log x a = logy a / logy x
In this equation x and y are constants (the two bases) and a is
a variable, thus dividing log y a by log y x is the same as multi¬
plying it by the constant 1 / log y x. So every N-log, which is
found by multiplying the log 10 of a number by a constant, is
simply a log, and all the rules that apply to logs apply equally
to N-logs, including the four basic rules:
log(XY) = log(X) + log(Y)
log(X/Y) = log(X) - log(Y)
log(X v ) = YX log(X)
log( Vx) = log(X) / Y
FINDING LOG(X+Y) WHEN LOG(X) AND LOG(Y) ARE
KNOWN: To allow all the numbers in a computer program to
be represented by N-logs, and to avoid the need for changing
N-logs to ordinary numbers, or the converse, a procedure is
needed that allows finding the N-log of the sum or differ¬
ence of two numbers directly when the N-log of each one is
known. Although it is not found in many modern textbooks,
such a procedure exists. It was invented in 1803 by an Italian
physicist named Leonelli, but was popularized by Gauss, and
called “Gaussian Logarithms” (see Ref. 1). Actually the logic
involved is quite simple, and the computer operations that are
required are reasonably fast and easy to implement. The
mathematical development of the formulas for accomplishing
this is shown in Appendix I, and the results for one family,
the Two-logs, are shown in Tables II, III and IV. Similar tables
for Three-logs would contain 300 lines each, 3000 for Four-
logs and so on.
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 7
403
TABLE II
Sum Factor for Two-logs
When A-B is
TABLE III
Difference Factor
for Two-logs. A-B < 30
Uhen A-B D
TABLE IV
Difference Factor
for Two-logs. A-B > 30
Uhen A-B is D
between:
S equals:
equals:
equals:
between:
equals
0
-
1
30
0
infinity
30
-
30
30
2
-
3
29
1
164
31
-
31
29
4
-
5
28
2
135
32
-
32
28
6
-
7
27
3
118
33
-
34
27
8
-
9
26
4
106
35
-
35
26
10
-
12
25
5
96
36
-
36
25
13
-
14
24
6
89
37
-
37
24
15
-
16
23
7
83
38
-
39
23
17
-
19
22
8
77
40
-
40
22
20
-
21
21
9
73
41
-
42
21
22
-
24
20
10
69
43
-
44
20
25
-
27
19
11
65
45
-
45
19
28
-
30
18
12
62
46
-
47
18
31
-
33
17
13
59
48
-
50
17
34
-
36
16
H
56
51
-
52
16
37
-
40
15
15
53
53
-
54
15
41
-
43
14
16
51
55
-
57
14
44
-
47
13
17
49
58
-
60
13
48
-
51
12
18
47
61
-
63
12
52
-
56
11
19
45
64
-
66
11
57
-
61
10
20
43
67
-
70
10
62
-
66
9
21
42
71
-
75
9
67
-
72
8
22
40
76
-
79
8
73
-
79
7
23
39
80
-
85
7
80
-
86
6
24
37
86
-
92
6
87
-
96
5
25
36
93
-
100
5
97
-
107
4
26
35
101
-
111
4
108
-
122
3
27
33
112
-
125
3
123
-
145
2
28
32
126
-
146
2
146
-
193
1
29
31
147
-
194
1
Above
194
0
30
30
Above
194
0
USING THESE TABLES: A “Sum Factor,” “S” and a
“Difference Factor,” “D” are defined by the equations:
A = Two-log(X)
B = Two-log(Y) where A > B.
S = Two-log(X+Y) - A
D = A - Two-log(X-Y)
With these definitions the Two-log of X+Y = A+S and the
Two-log of X-Y = A-S. To find the Two-log of X+Y, subtract
B from A, find the value of S in Table II which corresponds to
this difference, and add it to A. Similarly, to find the Two-log
of X-Y, subtract B from A, find the corresponding value of D
in Table III (if A-B < 30) or Table IV (if A- B > 30), and sub¬
tract D from A.
Examples: Some examples will show how this works out.
Suppose X = 1.479 X 10 12 and Y = 0.602 X 10 12 then
A = 1217, B = 1178, and A-B = 39. Since 39 is between 37
and 40, Table II shows that, in this case, S = 15, so Two-
log(X+Y) = A+S = 1217 + 15 = 1232. Since A-B > 30, D is
found in Table IV, and equals 23. Thus Two-log(X-Y) = A-D
= 1217 - 23 = 1194. As a check add X and Y: 1.479 X 10 12 +
0.602 X 10 12 = 2.081 X 10 12 , which has the log 12.32 and
the Two-log 1232. Similarly X-Y = 0.877 X 10 12 with the log
11.94, and the Two-log 1194, which results agree with those
obtained using the tables.
As a second example let A = -328 and B = -354 (-328 >
-354), A-B = 26. From Table II: D = 19, so Two-log(X+Y) =
-328 + 19 = -309. From Table III: D = 35, so Two-log(X-Y)
= -363. Checking this: X= 0.0005248, Y = 0.0002884, X+Y =
0.0008132 with the Two-log -309, and X-Y = 0.0002364
with the Two-log -363.
These examples clearly show the disadvantage of N-logs,
i.e., that addition and subtraction are more difficult when
using them, so that they would not be useful in contexts, as
in accounting, where these operations predominate. However,
Page 8
404
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
in most scientific calculations their advantages outweigh this
disadvantage. 1217 is easier to write and to pronounce than is
1.479 X 10 12 . To find the Two-log corresponding to 1.279 X
10 12 X 0.602 X 10 12 , 1217 is added to 1178, giving 2395.
The Two-log of 0.0008132 8 is 8 X -309 = -2472 and so on.
CAN LOGARITHMS BE USED TO REPRESENT NEGA¬
TIVE NUMBERS?: When it is proposed that N-logs be used
to represent all of the numbers in a series of calculations, an
objection that will immediately be raised by anyone familiar
with logarithms is the fact that, since there is no power to
which a base can be raised that gives a negative result, it is im¬
possible to take the logarithm of a negative number. While this
is certainly true it does not interfere with the use of logarithms
to represent negative numbers. Consider several comparable
situations. The simplest relates to the fact that decimal digits
alone cannot represent a negative number. Any group of sym¬
bols including only 012345678 and 9 will be interpreted as
a positive integer! Mathematical tradition, to get around this,
provides for the representation of negative numbers by the use
of an eleventh symbol, the minus sign. What’s sauce for the
goose is sauce for the gander! If extra symbols are allowed,
they can be used with logarithms just as well as with ordinary
numbers. Since the minus sign is already used to show whether
the logarithm is positive or negative, some other symbol, for
example the letter N, must be chosen to indicate that the
number represented by the logarithm is negative. Thus, since
the Three-log of 5678 is written 3754, the symbol for the
Three-log of-5678 could be written 3754N. The Three-log of
-0.3492 could be written -2457N, and so on. Of course the N
would have to be taken into account when using the S or D
routines described in the preceding section.
Another situation, very familiar to computer experts,
relates to the fact that any combination of the binary digits
0 and 1, taken as written, must be interpreted as a positive
integer. To get around this it is common practice in designing
and programming binary computers to represent a negative
number as the two’s complement of the corresponding positive
number. Thus the decimal number +55 would be represented
in binary by the symbol 110111, while -55 would be 001001.
This way of symbolizing negative numbers has two advantages.
Not only does it change them into a form the computer can
handle, it provides the added advantage that, within the com¬
puter, the addition of the binary number representing a posi¬
tive quantity to that representing a negative one will give a re¬
sult which is the difference of the two quantities (if the over¬
flow is neglected). This basic idea can be applied to N-logs,
as will be demonstrated in the next section.
N-LOGS FOR COMPUTERS: While there are many possi¬
ble ways in which a number language for computers could be
built around the N-log concept, one particular way of doing
this seems like a good one. It begins by assuming a 16-bit bi¬
nary word. This means that the largest number that can be re¬
presented is FFFF (Hex). Thus, including 0 there are 10000
(Hex), or 65536 (Decimal) possible numbers. There are four
possible kinds of N-logs to be represented; i.e., the + N-log
(i.e., positive N-log) of a + number; the - N-log (i.e., negative
N-log) of a + number; the + N-log of a - number; and the
- N-log of a - number. This means that the total number of
symbols allowable must be divided by four to find the largest
N-log that can be represented. 65536 divided by 4 is 16384
(Dec.) (= 4000 Hex)). If Three-logs were used this means that
the range of numbers that could be handled would be the ones
whose Three-logs extended from -16384 to +16384, i.e., the
numbers between 4.130 X 10~ 17 and 2.4210 X 10~ 16 . The
precision of all numbers would be that characteristic of Three-
logs, i.e., plus or minus 0.115%. This range of numbers and
this degree of precision is adequate for most scientific calcula¬
tions, so this approach seems to have practical appeal.
A SPECIFIC PROPOSAL: One way to implement this idea
would be to select the lowest group available in a 16-bit word
(i.e., the numbers from 0000 to 3FFF (Hex)) to represent the
positive Three-logs of positive numbers. The two’s comple¬
ments of these (i.e., the numbers from FFFF down to C001
(Hex)) would then logically represent negative Three-logs
of positive numbers. Adding 4000 (Hex) to the lowest group
would set aside the numbers between 4000 and 7FFF (Hex)
to represent positive Three-logs of negative numbers, and their
two’s complements, the numbers from C000 down to 8001
(Hex), to represent the negative Three-logs of negative num¬
bers. Such an approach would provide a simple way of arriving
at the initial Three-log, by the use of a scientific calculator,
simple algorithms within the computer for converting these
input numbers to the corresponding binary numbers, and ex¬
treme simplification of the operations of multiplying, dividing,
powers and roots by the computer. Operations corresponding
to the addition or subtraction of the original numbers, or the
intermediate results, would be a little more complicated, re¬
quiring look-up tables for S and D, but would be perfectly
feasible and quite fast.
CONCLUSION — A PERSONAL NOTE: It must be obvious
to anyone who reads through this paper that the missing step
is the creation of a program, which must be in machine lan¬
guage to be effective, demonstrating how well these ideas
work. I have not attempted this for a very good reason. I have
been trying for somewhat more than ten years to get across
the (to me) obvious advantages of a wider use of logarithms,
and am fully conversant with the mathematical side of the
story. My acquaintance with computers, on the other hand, is
limited to building my Digital Group unit, using it extensively
for computing, preparation of text (including the manuscript
for this paper) and plotting. All of this has been programmed
in Basic. Up to now I have not found the time to get into ma¬
chine language programming. In short, if the subject matter of
this paper is to be proved properly, I need help. If any reader
with the appropriate skill finds the subject appealing, I would
be most anxious to work jointly on proving these ideas. The
fundamental concept of N-logs is sound, and there is no
doubt in my mind that they will make a valuable addition to
computer techniques, but this needs to be proved. □
APPENDIX I
The Mathematical Basis for the Sum and Difference Factors
Note: In what follows it is assumed that X>Y. Antilog(a) is
used to mean the result of raising the logarithmic base to the
power “a”, i.e., the inverse operation to log(a).
Let: A=log(X) B=log(Y) and C=A-B
Then: antilog(C)=X/Y
Let: H=Y/X=antilog(B-A)=antilog(-C)
The Development of the Sum Factor "S":
log(X-Y)=log[X(l-Y/X)]=log(X)+log(l-Y/X)
Let: S=log(l+Y/X)=log(l+H)
Then: log(X+Y)=A+S
The Development of the Difference Factor "D":
log(X+Y)=log[X(l+Y/X)]=log(X)+log(l+Y/X)
Let: D=-log(l-Y/X)=-log(l-H)
Then: log(X-Y)=A-D
(continued on page 36)
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 9
405
$$$$$$$$$$
MS UEEHS
SraSLBT
asp/m
gama masltiis pgiam
using
Flaaftiurifar I graphics
Page 10
406
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
iiiiiimiiminmiiM (iimiiiiiiim'
© by David W. Friedman
Eiko and I were spending the year-end holidays quietly
at home with my word-processing-oriented North Star
patiently waiting for the next major copywriting assignment
which is how I earn our keep. We had been recounting the fun
of playing the slot machines in Macau and the Philippines
when she challenged me to put the game up on the computer.
I agreed on the condition that she help with the graphics and
off we went.
VIDEO BIT DIAGRAM
fiIIS;yiD+4ppH yiD
76543210 76543210
1111 xxxx xxxxxxxx
• • • !_pix»ls on/off ! S S__graphics pixel bits
• _horizontal I I_non-graphic bit <40H
!thin lines I_reverse video bit
8 !_vertical
!_half-intensity shading
THE HARDWARE
A North Star Horizon II double-density system with 56K
of RAM, a Vector Graphics Flashwriter I video board at EOOO,
a 12V TV converted to a monitor and an 80-column friction-
feed Teletype 43. Other video boards may have the same or
similar graphics provisions but I know of at least two which
don’t, so you’ll have to check carefully or else rewrite the
graphics routines to match what you have.
THE SOFTWARE
The designation of each bit is shown. Note that bit 6
(40H) of the video byte is undefined in the graphics mode;
this bit has two graphics coding uses in the VEGAS program.
The attribute bytes are actually equipped with RAM only
for the lower nibble such that, for normal alphanumeric
character usages, reading this memory will give an FO hex
byte. This is slightly inefficient usage of address space but, for
an 8-bit microprocessor, yields efficient access to the remain¬
ing four attribute bits.
Las Vegas Super-Slot is programmed as a standard CP/M
transient at 1OOH and requires CP/M both for loading and for
internal file manipulations as well as input/output standardiza¬
tion. I have been running VEGAS.COM using a modified
version of the MENU.COM program by James Frantz which
appeared in Creative Computing’s December 1979 issue.
On both cold and warm starts, MENU is invoked so the user
need only type a 2-digit number to access VEGAS.
THE GRAPHICS
Flashwriter I is an excellent video board for alphanumerics
with limited graphic capabilities. Characters can be displayed
as 16 lines of 64 characters per line. The graphics capability
can be invoked randomly for any desired character positions
which further subdivides each character location into a 3
high by 2 wide pixel (picture element) array. This yields an
overall resolution of 128 pixels horizontally by 48 pixels
vertically.
There are also four other graphics features each controlled
by an isolated bit: reverse video, low intensity video, horizon¬
tal thin lines and vertical thin lines. Access to the twelve video
bits for each character position is segregated into two memory
areas which can be called video and attributes (VID and
ATTB) such that each character-position’s attributes are
always exactly four RAM pages above the corresponding video
byte. For example, if the board is located at EOOOH, the first
character position’s video byte will be at EOOOH while the
four excess attribute bits will be located in the byte at E400H.
David W. Friedman -2 -8-24 Okubo, Shinjuku-Ku, Tokyo,
Japan 160
USING THE GRAPHICS
VEGAS begins by setting its own stack pointer, thus
discarding the entry stack pointer, and calling the routine
INITIZ which handles all necessary initialization, including
graphics. VEGAS provides the user with a 3-reel/3-position
down-rotating-reel presentation of a slot-machine plus a
moving crank arm at the right and various status displays
including winning combinations, current credits, current
winning amount, current jackpot amount, ready indicator
and others depending upon the current operating mode:
TEST, PLAY, ZERO or READY. The initialization of the
graphics functions is in the following order:
+ ERASE the screen to all spaces, 20H
+ apply the PAY OFF strings at top and bottom
+ apply left WIN and right CREDIT boxes
+ apply shading to top and bottom reel positions
+ apply graphics bits and REEL boxes at three positions
+ apply TICKS at centers of boxes
+ apply initial reel patterns using SPIN subroutine
+ apply operating arm using CRANK subroutine
+ show JACKPOT amount retrieved from separate file
or create file and load it with 100 credits
There are several very generalized routines used to accom¬
plish the above and usage of these is described here:
+ at entry, the B/C register must contain: either BLKOFF
=0 or BLKON=8080H plus 100H times the vertical
height (to B) plus the horizontal width (to C) defining
an area.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 11
407
Number 50
+ at entry, the H/L register must contain: the beginning
character position byte which is: either VID or ATTB
plus the vertical line (0 to 15) times the linelength
(LNLGTH=64) plus the horizontal character position
(0 to 63).
+ BOXY requires at ATTB address in H/L to apply or
remove a rectangular box dimensioned by B/C. Exceed¬
ing right or bottom limits does not wrap around nor
write into non-graphic RAM addresses. BOXY uses
the GRAPH and GPHRHZ routines and may be used
for zero width or height boxes (lines only) although
VEGAS does not contain such usages.
+ GRAPH requires an ATTB address in H/L and the bit
of interest in the A register to apply or remove that bit
from the rectangular area defined by B/C. GRAPH
uses the GRAPHER routine.
+ GRAPHON is the same as GRAPH with A being set by
the routine to the graphics bit, 0001B.
+ GRAPHER applies bits to one horizontal line at a time
+ GPHRHZ is the same as GRAPHER with A being set
by the routine to the horizontal line bit, 0010B.
In addition to these generalized routines, two specialized
routines are used:
+ CRANK which calls HANDON and HANDOF both of
which call the generalized BOXY routines.
+ MVPTN2 which requires the area to be specified in
B/C and the upper-left byte to be specified in H/L.
MVPTN is set for areas 10 characters wide by 12 high
and thus moves 120 bytes to the block of video memory
specified.
These routines provide access to every graphics capability
of the Flashwriter I video board and are readily applicable
to use within other, unrelated programs.
FORMING THE GRAPHIC PATTERNS
REEL GRAPHICS PATTERN CREATION FORM
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Having settled upon the graphic presentation desired, it is
only necessary to code the individual bytes by referring to
the form’s coding diagram wherein each pixel’s bit value is
given in hexadecimal; adding gives the byte value. VEGAS
uses 3FH for all white pixels within a character position
rather than the optional reverse video function 8 OH. Bit 6
which has value 40H is reserved for identification coding of
the patterns and is added to the first four bytes of the pattern
for this purpose. In this way, the final pattern’s code can be
read out of the video memory after the reels have stopped.
As an aid to rapid creation of the reel-graphics, the form
shown was very efficient. It incorporates a pixel aspect ratio
of 1.7:1 compared with about 2:1 actually obtained (depend¬
ing upon monitor adjustment) such that penciling-in the de¬
sired blocks yields a very slightly squat but proportional black
on white representation of what the final pixel pattern will
look like when shown on the video screen. However, it was
found that short video display routine to test the final ap¬
pearance was essential to finalize the individual patterns.
THE MAIN PROGRAM
After “READY” is shown, the KEYTEST routine looks for
any keypress while incrementing the B/C register. When a
keypress is obtained, C is saved as a RANDOM number before
returning. The key is read to register A and tested against
‘$’ (credit entry) and the first letter of the four keywords
EXIT, TEST, ZERO and PLAY before testing for a CR. Any
of these routines, if called, will return with a CR in A if the
call was inappropriate, thus executing an ACCEPT/OPERATE
cycle. Keywords are control key oriented by ANDing each
reference string letter with CTRL=1FH and represent pass¬
words to be known only to the user and not to the players.
+ ‘S’ issues credits only if no credits remain. If credit is
issued, the jackpot is increased by about 15% of the
credited amount up to a maximum of 15 jackpot credits
while receipts are increased by the full credited amount.
+ EXIT erases the entire video memory and saves the
jackpot and receipts before branching to a CP/M warm
start.
+ TEST applies 100 credits and automatically runs the
game until credits reach 0 or until the CR key is pressed.
Jackpots are not paid in TEST and it returns with
credits set to 0 in either case and can be used to cancel
a winning player’s credits.
+ ZERO sets receipts accumulated from ‘S’ collections
to 0, shows 0 receipts, saves the jackpot and receipts
and, upon pressing the CR key, restores the READY
condition. This feature allows the user to leave a player
in charge with means to check the receipts when he
later returns. (continued on page 14)
Page 12
408
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
+ PLAY shows current receipts from "$’ collections,
saves the receipts and jackpot and, upon pressing the
CR key, restores a READY condition without having
affected the current credits.
ACCEPT checks to make sure credits are available before
permitting OPERATE to be called. If credit is available, the
READY sign is removed and OPERATE is called. If OPER¬
ATE returns with the carry set, the jackpot is paid out and a
zeroed jackpot is saved to disk. All internal branches are back
to MAIN which restores the READY mode.
THE OPERATE ROUTINE
One credit is CHARGEd for each play, the winning value
is zeroed, the arm is CRANKed with sound effects, SPEED
sets maximum reel running times based on the RANDOM
number generated during KEYTEST, the reels are spun with
stopping sound effects and options for individual reel—stop¬
ping control using keys ‘1’, ‘2’ and ‘3’, a WINCHeck is per¬
formed which increases the jackpot for certain high payoff
combinations, the winning amount is shown and, if not zero, is
CREDitedOUT through one-by-one adding to the credits
with sound effects. CREDOUT returns with the carry set if the
win was three bars in order to pay out the jackpot.
THE SPIN ROUTINE
Here, speed of ‘rotation’ is very important. The use of a
fast pattern stuffing routine and video pattern internal indenti-
fication coding were necessary to obtain sufficient speed
even with the North Star’s 4MHz Z-80, although no attempt
was made to use any of the special Z-80 move instructions
since these are not compatible with CP/M’s assembler. If run¬
ning on a 2 MHz 8080A, this routine’s code can be expanded
to eliminate internal subroutine calls which will help some¬
what.
Initial entry is at SPIN 1 with 12 in the A register to insure
the movement of at least 3 patterns before STOP-KEY check¬
ing. SPINCouNT and each of the REELnS global variables
must be maintained at multiples of 4 to keep the patterns
centered on the TICKS at the middle position of each reel.
SPEED presets the globals prior to SPIN entry and multiples
of 4 pattern movements insure synchronization.
If any reel is stopped while others continue to spin, the
extra time must be taken up to avoid speed increases of the
remaining spinning reels and this is the function of the calls
to TIMER 1 in the SPINER routine. The last 16 counts of the
REELnS globals are sub-divided into four sets of which three
invoke TIMER 1 to fill time and one outputs a space to the
printer for sound effects in addition to advancing the pattern
by 1/4 which gives the slowing-stop with sound effects. The
pattern for the CHERRY has non-graphic 40H start byte and
signals the RESETP section of SPINER’s code to reset the
pattern to CHERRYY in order to close the pattern loop
similarly to what would exist on an actual slot machine reel.
STOPCMP checks the REELnS globals for the required all¬
zero stopped return condition. STOPKEY checks for a key-
Page 14
press of ‘1’, ‘2’ or ‘3’ and adjusts the respective REELnS
global variable to bring about a stop with slowing and with
‘slip’ determined both by the reel number and the RANDOM
number generated at the start of each cycle by MAIN’s
KEYTEST. Multiples of 4 must be maintained and register
A is set to 8 to introduce a minimum time interval between
acceptance of STOPKEY presses prior to jumping back to
SPIN 1.
THE WINCHECK ROUTINE
WINCHK ‘reaches’ into the video memory and extracts
the 2nd through the 4th byte’s 40H bit identification codes
with BYTINA. The 3 reel’s bytes are stored in E, D and A
respectively. Comparisons and BAR substitutions are used
to determine winning combinations with winning values
taken from the PAYTaBLe. The winning amount is saved as
the VALUE global and, depending upon the amount, an ad¬
dition is made to the jackpot.
BIOS AND BDOS CALLS
All BIOS console calls and printer calls are made directly
to the BIOS branching table whose high byte is obtained
from the warm start address stored in the jump at OH. Disk
operations to create and manipulate the incidental jackpots.lot
file, use the normal BDOS calling convehtions except, upon
return from every BDOS call, a dental jackpots.lot file, use the
normal BDOS calling conventions except, upon return from
every BDOS call, a check is made to see if an error occurred.
In case of a BDOS error, the graphics initialization is destroyed
so an error message is shown indicating return to CP/M via a
warm start.
SHOWING STRINGS, NUMBERS AND MATCHING
KEYWORDS
All strings are terminated with nulls. The SHOSIG routines
detects the null for return after advancing the D/E string
pointer so that a subsequent call can be made to show another
string following the null without resetting the pointer. Reverse
video is built-into the strings for READY and JACKPOT.
All changing numbers are shown as 5-digit integers using
SH05DIG which can suppress leading zeros if entered with
b = 0. Leading zeros are suppressed for WINS but are retained
for all other changing numbers.
All MATCH strings are ANDed with CTRL=1FH to
invoke the need of pressing the CTRL key with all of the key¬
word letters and, each string is terminated with a null. The
MATCH routine returns with the zero flag set if successful
or not set if there was no MATCH.
LISTING AND AVAILABILITY OF DISKS
The complete CP/M assembly listing follows except for the
data bytes representing the reel patterns which are printed as
a memory dump using CP/M’s DDT in order to save printing
space. If you’d like to save yourself the typing time and associ¬
ated errors, I can make the VEGAS.ASM and VEGAS.COM
files available but only on North Star 10-hard-sectored
disks for $50 and, I’ll assemble VEGAS.COM to your selected
video location of the Flashwriter I board if you mention it.
CONCERNING WINNING STATISTICS
If one discounts the effect of using the three number keys
(1,2 and 3) to control the stopping of the reels, the ‘payback’
expectations are as summarized here. However, it is possible
to ‘help’ things along by using these 3 keys.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
409
EXPECTATION TABLE
ITEM
1
COMB.
PAY
EXP.
JBONUS
JKPOT
BARS
2
8
250+J
2000
0
0
MELONS
2
24
100
2400
13
312
DOLLARS
2
2-4
50
1200
7
148
BELLS
A
112
20
2240
3
334
PLUMS
4
1 1 2
14
1548
2
224
ORANGES
5
1 85
10
1850
0
0
CHERRIES
3
57
10
570
0
0
first 2
207
5
1 035
0
0
first 1
1 380
2
2740
0
0
LEMONS
5
1 85
0
0
1
1 85
CHARGES
0
< 1 46)
0
0
3 438
STOTAL
27
2294
- -
1 5423
—
1443
NO UINS
—
17389
0
0
1
•
JACKPOTS
< 8)
208
1444
1
_1
TOTALS
27
1 9683
—
17287
1 7287
PAY BACK=
87.8
percent
19483
(skill not
c onsidered>
While our experience has shown that practice time tends to
yield a higher percentage of bigger wins, at the same time the
number of credits required to obtain these wins increases! This
is caused by the player trying to lineup the reels, as they fly
by, using readily recognizable patterns such as bars and dollar
signs but, because of the reel ‘slip’ factor introduced by
STOPKEY as a function of the RANDOM number, he is
generally one pattern away from success. Not wanting to dis¬
turb his progress in hand, the player keeps trying to adjust
for the single offset of the patterns and is thus, barring good
luck, more often than not defeated. It would be blatantly
untruthful to claim that this was not a planned perversity of
the VEGAS game machine.
In view of the above, it can be said that there is the pos¬
sibility of skillful manipulation of the game but, just as in
real life, the most skillful approach may not yield the most
profitable result. Eiko and I do hope you will enjoy playing
the LAS VEGAS SUPER-SLOT game machine as much as we
do. □
REEL GRAPHICS PATTERN CREATION FORM
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Number 50
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Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia
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Page 22
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
417
by Leonard E. Garcia
EUlCrV^El
] I lLMH STFH EF1SI3
1 STFUEfflEflT SEflENFETEN
QUICK-KEY is an 8080 assembly language program that
generates North Star BASIC commands and statements from
pre-stored text in memory by using a two key command.
The program also allows a user to enter and define any
text that will be sent to the North Star BASIC interpreter
(or any system program) upon hitting a special sequence
of keys.
Commonly entered routines, answers to prompts, even
entire routines can be entered into the program and sent
to any program that calls for a character from the terminal
by just hitting two keys. A user no longer needs to enter the
same information again and again.
As written, the QUICK-KEY program contains commands
and statements which are used by the North Star BASIC,
but the text can be changed by the user interactively and you
can make copies of the program containing text for an assem¬
bler, text editor, user program, etc.
The text is stored in blocks of 32 characters, and the
statements or text are accessed by hitting the sequence:
ESC x
where ESC is the ESCAPE key and the x is a letter key in the
range of A thru Z.
Once the program is executed in high memory, it will lo¬
cate the address of the user’s Character-In routine in the
North Star DOS, patch it into its own routines, re-route the
Character-In “calls” to itself and then return to the Disk
Operating System. The program will then scan all keyboard
entries for the ESC x sequence code to send the text to what¬
ever program called for a character from the terminal.
Thus, the sequence: EscA
will send the text: ABS (Absolute)
to the BASIC interpreter, and display on the screen as it is
being echoed by the system. A second ESC will cause the first
text, ABS, to be rubbed out and the next statement that
starts with “A” to be sent:
APPEND
Continuing to hit the ESC key will send the next command
of the “A” series, deleting the last that was sent. Once a
space or another character other than ESC is entered, the key
Leonard E. Garcia-3517 Herschel Ave., Dallas, TX 75219
Number 50
418
code is then voided and another ESC x sequence may be
started to generate a different text.
For example, the statement
100 IF A1 = 0 THEN GOTO 300 ELSE PRINT “TEST”
may be generated with the sequence:
100 EscI A1 = 0 EscT EscGEsc 300 EscE EscP “TEST”
Note that EscG will generate the text “GOSUB”. Since
the statement we wanted was “GOTO”, another ESC was
entered to rub out the “GOSUB” and send the “GOTO”
instead.
Should you wish to use spaces to indent a program, the
sequence:
Esc (Space bar)
will send 5 blank spaces to the BASIC interpreter. Another
immediate ESC will rub out the first 5 and send 10, and a
third will rub the last 10 and send 15 spaces. The ESC (Space
bar) will in fact act as tabs to enter a formatted program
listing.
CUSTOMIZING.
Keys H, J, Q, U, X, Y and Z do not have any corresponding
BASIC statement or command stored under them and are
available to the user for any custom text. QUICK-KEY
will accept, in its customizing mode, text to be stored and
defined under ANY key. This text may exceed the 32 char-
acters/key that is allowed, but the key code for the next
block of text will be overlaid and cannot be used.
When entering the customizing mode, hit “C” when the
program asks for a command. It will then ask: “FOR KEY
LETTER (A THRU Z)?”, enter the letter and a format will
appear as a guideline to entering the text:
.31 char .
If the text = NOW IS THE TIME FOR ALL GOOD MEN TO
WRITE PGMS (Ctl-C) is entered under key code “X”, then
hitting EscX later will send the entire text to the interpreter;
while hitting EscY will only send the portion “TO WRITE
PGMS”, since it starts at the 33rd character. This feature may
be used to send a name and address to a program or address
only, etc.
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Another method of customizing text is by use of delimi¬
ters. The semi-colon (;) is used to signify to the program the
end of characters. Thus an entry formatted as:
NOW IS THE ;TIME FOR ALL;GOOD MEN (Ctrl-C)
under a key code letter “Z”, will send text as follows:
EscZ = NOW IS THE
Esc = TIME FOR ALL (Rubbing out the “NOW IS THE”)
Esc = GOOD MEN (Rubbing out the “TIME FOR ALL”)
When customizing text in this mode, the last character
you enter MUST BE A CONTROL-C. This will indicate to
the program then end of text for that key letter.
More than one line of text is allowed, with the carriage
return being sent along with the text to the BASIC interpreter.
Thus the custom text:
1000 REM—COMMON USE ROUTINE—
1010 FOR A = 1 TO 10
1020 PRINT “ ”
1030 NEXT A
1040 RETURN
(Ctrl-C)
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may be stored in memory under any desired key A thru Z.
Of course, long text will overlay the existing text, but it is
easy enough to have various copies of the QUICK-KEY
program with different text.
THE PROGRAM.
... is assembled at 9A00H. This is the highest in memory
that it can be assembled for a 32K North Star system with
memory starting at the standard 2000H. The customizing
routines, commands, etc., reside in the lower part of the
program and can be overlaid by a user program once the QUICK-
KEY is operating. However, since NS BASIC places temporary
data at the highest address for which it has been set, it must
be “MEMSET” after it has been loaded in memory to an
address no higher than 39880 (decimal). This will prevent it
from overlaying the functional part of the program. This
reminder will be displayed by the program.
After any text has been entered into memory in the cus¬
tomizing mode, and ended with a CTRL-C, the program will
return to the command mode. Once the patch is effected with
the “E”, (EXECUTE) command, it will re-route the user’s
I/O routines and cannot be jumped to or customized again
unless the I/O has been restored to it’s original configuration.
This is done with the sequence EscO. This command will
restore the I/O and then the QUICK-KEY program will be
inoperative, no longer scanning the keyboard inputs.
So, the normal procedure is to:
1. With your North Star DOS loaded, execute the program
from disk.
2. If any customizing is required hit “C”.
3. If none is desired, or if you are thru customizing, hit “E”
to patch the I/O.
4. After the program has returned to DOS, execute your
BASIC interpreter and limit the memory it can use with
the “MEMSET” command.
5. Use the program, when done hit EscO to restore the I/O.
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Please remember that this program sends data in to DOS,
BASIC or any other program that uses the North Star DOS
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Page 24
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
419
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Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
421
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Number 50
422
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 27
FRENCH
TRES BIEN!
BICYCLE=LE VELO
MAIS NON!
SUBWAY=LE METRO
HOUSE=LA MAISON
ROOM=LA CHAMBRE
RABBIT=LE LAPIN
HELICOPTER=L' HELICOPTERE
FLOWER=LA FLEUR
MUSHROOM=LE CHAMPIGNON
SNAIL=L' ESCARGOT
WINE=LE VIN
TRAIN=LE TRAIN
CHEESE=LE FROMAGE
LISTING
PROGRAM TUTOR
THIS IS A PROGRAM TO PROMPT THE STUDENT TO SPELL WORDS IN A
LANGUAGE WHEN GIVEN A WORD IN A DIFFERENT LANGUAGE.
BY: GARY D. GAUGLER 5706 SEASCAPE. CITRUS HEIGHTS, CA 95610
IMPLICIT INTEGER (A-Z)
COMMON LINE(80),KOL,MXKOL
DIMENSION LANG1(20),LANG2(20),ERROR(20),IANSC20)
DIMENSION LANG(20),JPROMP(5),CORECT < 20),NCOREC(20)
DATA CARAT,SPACE / 1H~, 1H /
DATA JPROMP /2H W.2H0R.2HD ,2HF0,2HR /
. FETCH OUR LANGUAGE FILE IF IT EXISTS
OPEN (UNIT=2,NAME='DK1:FRENCH.DAT',TYPE='OLD',
1 ACCESS*'SEQUENTIAL')
DIRECT=0 !0=ENGLISH—>FOREN
MXTRY=2
TYPE 10
FORMAT (IX,"DO YOU WANT TO ENTER FOREIGN FOR ENGLISH? (Y/N) ',*>
READ (7,20)ANSWR
FORMAT <A1>
IF (ANSWR. EQ. ' N ' ) DIRECT= 1 ! FOREN—>ENGL I SH
. GET FILE'S LANGUAGE BASE AND MESSAGES
CALL INPUT
CALL NAME(LANG,LENLAN)
CALL INPUT
CALL NAME(CORECT,LENOK)
CALL INPUT
CALL NAME(NCOREC,LENBAD)
. READ A WORD-PAIR
CALL INPUT
FORMAT (20A1)
. CLEAR-OUT THE ARRAYS
DO 120 1=1,20
LANG1(I)=SPACE
LANG2<I)=SPACE
ERROR <I)=SPACE
IANS(I)=SPACE
. GET LANGUAGE WORD
CALL NAME < LANG1,LEN1)
. NOW GET THE SECOND LANGUAGE WORD
CALL NAME(LANG2,LEN2)
. NOW PRESENT A WORD TO THE STUDENT
NTRY=0
IF (DIRECT.EQ.1) GO TO 350 !FOREN—>ENGLISH
KOL= 1
DO 325 J=1,LENLAN
LINE(KOL)=LANG(J)
K0L=K0L+1
DO 330 J=1,5
N2=JPROMP(J)
N1=N2/256
N2=N2-256*N1
LINE(KOL)=N2
LINE(KOL+1)=N1
K0L=K0L+2
DO 335 J=1,LEN1
LINE(KOL)=LANG1(J)
K0L=K0L+1
DO 340 J=KOL,40
LINE(J)=SPACE
TYPE 40,(LINE(J),J=1,40)
FORMAT (IX,'TYPE THE ',40A1>
GO TO 400
tutor :
A
FOREIGN
LANGUAGE
VOCABULARY
TRAINER
by Gary D. Gaugler
This program is designed to be the
basis of a foreign language instruction sys¬
tem. When run on a single-user system,
the user can practice, learn and build a
foreign language vocabulary. When in¬
stalled on a multi-user system, many stu¬
dents can simultaneously use the pro¬
gram. Further, each student user can be
practicing a language different from the
other users.
The program presents a foreign lan¬
guage word to the student and waits for
the student’s response. The words are
retrieved from a disk file which contains
words in English and their associated for¬
eign equivalent. The file also contains a
header indicating the foreign language,
a character string to be displayed when a
correct response is made and a string
which is displayed when an incorrect
response is made. The program also per¬
mits the student to practice English-
foreign or foreign-Enghsh. The student
replies to the program’s prompt for the
desired direction.
When a word is presented, the pro¬
gram checks each character of the stu¬
dent’s response for correctness. For each
character which does not match the
correct response, an up-arrow (t) is
placed below it, indicating an incorrect
character response at that location. The
student has one more chance to respond
before the program moves on to the next
word.
The program, called TUTOR, is writ¬
ten in PDP-11 FORTRAN-IV for RT-11.
This version of FORTRAN is very similar
to FORTRAN-66 so one should have
Gary D. Gaugler-5 706 Seascape Court,
Citrus Heights, CA 95610
Page 28
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
423
little difficulty adapting it to any system
which has a FORTRAN compiler.
Included with the program’s listing is
a sample language file for French. Using
this as an example, other language files
can be made. The first line defines the
language for which the specific file is in¬
tended (the example is FRENCH). The
second line will be displayed verbatim
when a correct response is made. The
third line will be displayed verbatim when
an incorrect response is made. The re¬
maining lines are the English-foreign
word pairs organized as: English=foreign.
The equals sign delimits the English and
foreign words. Embedded spaces are sig¬
nificant and must be included for a cor¬
rect response.
I would be pleased to provide a floppy
copy of the program to those sending a
formatted diskette (RX-01 or RX-02)
and return postage and container. I also
welcome communicating with others
interested in PDP-11/LSI-11 hardware
or software. □
0054
C
350
TYPE 50 » (LANG2( I), I * 1,LEN2 )
0055
50
Q
FORMAT (IX*"TYPE THE ENGLISH WORD FOR ',20Al/>
c....
CHECK FOR CORRECT WORD & SPELLING
0056
400
READ (7*35)IANS
0057
JERR-0
0058
DO 425 J*1 * 20
0059
IF (DIRECT.EQ.1) GO TO 410
0061
IF (LANG2(J).EQ.IANS<J) ) GO TO 425
0063
JERR=1
0064
ERROR(J)*CARAT
0065
GO TO 425
0066
410
IF (LANG1(J).EQ.IANS(J)) GO TO 425
0068
JERR-1
0069
ERROR(J)=CARAT
0070
425
q
CONTINUE
C. . . .
REPORT IF OK OR AN ERROR
0071
IF (JERR.EQ.1) GO TO 500
0073
TYPE 60 » (CORECT ( J ), J=1 , LENOK )
0074
60
FORMAT ( IX,//,1X.20A1/)
0075
q
GO TO 110
C. . . .
ERROR
0076
500
TYPE 65 , ERROR ,( NCOREC < J ), J=1 , LENBAD )
0077
65
FORMAT ( 1X.20A1//,1X,20A1/)
0078
NTRY*NTRY+1
0079
IF (NTRY.LT.MXTRY) GO TO 320
0081
GO TO 110
0082
END
Thanks go to Carol Newhouse for sup¬
plying the French vocabulary.
SUBROUTINES
0001
p
SUBROUTINE INPUT
L
c
p
THIS SUBROUTINE READS ONE LINE FROM THE DISK FILE
0002
COMMON LINE(80),KOL * MXKOL
0003
c
DATA IBL /1H /
0004
c
KOL= 1
c... .
READ A LINE FROM THE LANGUAGE FILE
0005
READ (2,30,END*900)LINE
0006
30
p
FORMAT (80A1)
L
c... .
DETERMINE THE LAST USEFUL COLUMN
0007
DO 200 1*1,80
0008
IF (LINE(I).EQ.IBL) GO TO 200
0010
MXKOL*I
0011
200
CONTINUE
0012
RETURN
L
c.. . .
END OF DATA FILE
0013
900
STOP
0014
END
Gary Gaugler is currently a computer
system designer at McClellan AFB, CA.
His background includes hardware and
software design, analysis and construc¬
tion. He was previously an IC design en¬
gineer and system architect at the Air
Force Avionics Laboratory, Wright -
Patterson AFB, OH. He was involved in
IC development, microprocessor design
and development and software engineer¬
ing. His interests are IC design, computer
simulation of electronic circuits and hard¬
ware design.
0001
SUBROUTINE NAME(IOUT,NCHARS)
c
c
THIS SUBROUTINE READS A WORD FROM THE INPUT LINE
c
INTO THE ARRAY PASSED AS AN ARGUMENT (IOUT). THE LENGTH
c
p
OF THE WORD IN CHARACTERS IS RETURNED IN 'NCHARS'.
0002
L
p
COMMON LINE(80),KOL,MXKOL
0003
L
DIMENSION IOUT(20)
0004
p
DATA ICM.IEQ /1H,, 1H=/
0005
NCHARS=0
0006
IK0L=1
c
c.. . .
BUILD THE WORD IN 'IOUT' UNTIL TERMINATOR ENCOUNTERED
0007
100
IF (KOL.GT.MXKOL) GO TO 900
0009
IF (LINE(KOL).EQ.ICM) GO TO 900
0011
IF (LINE(KOL).EQ.IEQ) GO TO 900
0013
IOUT(IKOL)=LINE(KOL)
0014
K0L*K0L+1
0015
IK0L=IK0L+1
0016
NCHARS=NCHARS+1
0017
p
GO TO 100
L
c.. . .
END OF WORD FIELD
0018
900
K0L=K0L+1
0019
RETURN
0020
END
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
424
A/
END
Page 29
INTERFACING THE WH14 PRINTER
to your microcomputer’s serial port
is simpler than you think
by Lachman Sippy
What is wrong with this relatively inexpensive feature
loaded printer? I ask this question because I have read so many
articles or letters from disappointed or frustrated owners of
the WH14.1 will describe my own experience and tell you how
to get the most out of it.
I acquired a WH14 printer at a bargain price from the
recent Microage redistribution list. According to them, it was
in perfect working order except that it was missing the RS232
cable and it was out of warranty. Since the serial port on
my own system does not have handshaking,* I wired only
four RS232 signals, namely RS2320UT(2), RS232IN(3),
signal ground(7) and protective ground(l). Several off-the-
shelf serial I/O boards do not use the handshaking signals
including Morrow’s Switchboard, North Star serial ports,
3P + S.
To my delight, the printer worked. However, above 300
baud, it became evident that one must use handshaking.
I was determined to try all possible ways to avoid that so I
tried delays after C/R, after each character output, but to no
avail. It seemed that I have no choice but to use the RTS(4)
or the DTR(20) RS232 signals to provide for handshaking,
via one of the parallel ports on my system. On reading the
manual again, I noticed that the WH14 also provided hand¬
shaking via the output side of the same serial port. Simple,
when the printer is not ready for any reason it sends a
CTL-S(13H), and when ready it outputs a CTL-Q(llH).
These signals are evidently sent on a continuing basis at the set
baud rate. I programmed a new output driver to test the input
status and if a character is received it tests for a 13H. If a 13H
is received I wait in a loop until an 11H is received before
sending the character to the printer. With this simple driver the
printer works at all the available baud rates without losing any
data. As the reader will note, having this ability to do the
handshaking with software via the same serial port makes the
WH14 extremely versatile, and one should have no problem
connecting to any microcomputer.
The WH14 operations manual indicates that it is normal
for the printer to occasionally stop printing even though
the printer is not out of paper, there is no paper jam, and the
print head is still cool. By simply using the on-line key (re¬
leasing the key and then depressing it again) the printer is
restored without losing any characters. This is true and it
works with the driver that is mentioned here. However, I
wish that Heathkit or Zenith would do something about it.
With all the intelligence in the printer, a modification to then-
software in ROM, the printer should reset itself.
I should mention an additional problem that I encountered
with my printer. It turned out that when my printer stopped
* The term “handshaking” refers to a pulse exchange be¬
tween the CPU and asynchronous communicating peripheral
device/s. Handshaking establishes synchronization and ensures
proper operating.
Lachman Sippy - Box 1107, 2000 Center Street, Berkeley,
CA 94704.
for no apparent reason, my use of the on-line key as de¬
scribed in the previous paragraph had no effect. In fact,
when the printer stopped, I was unable to recover even if
I powered off. My diagnosis of this failure led me to believe
that I had a problem with the baud rate generator on the
WH14’s 8250 UART. I determined this by querying the input
from the WH14. What I would receive was strings of l’s and
0’s in various combinations. Since I was not absolutely sure
that it was a baud rate problem, I was about to take it to the
local Heathkit service center. The cost to fix it would be
$65.00 plus parts. The price of a replacement 8250 was
approximately $14.00 from Heathkit. I decided to take a
chance and bought one in spite of the fact that they said they
did not take back ICs once sold, even if it was defective,
because it was sure to be good. I was surprised at the way
the salesman handled the MOS chip, probably out of sheer
ignorance. Anyway, after I replaced the 8250 on my printer I
had no further problems.
To sum up, it appears that the WH14, due to its versatility,
is a good buy for the price, assuming that it proves to be reli¬
able in the long run. The sample code for the driver follows.
The code assumes serial port on the Morrow’s Switchboard
with the I/O base address set to 20H, and the data to be out¬
put in the C register.
STAT = 22H
DATA = 21K
PDA = 40H
THE * 80H
NPAR = 7FH
CTLS = 13H
CTLQ = 11H
0000
DB 22
DRVR:
IN
STAT
;Get input status
0002
E6 40
ANI
RDA
;Data avail?
0004
CA 0000
JZ
DOUT
;No, continue
0007
DB 22
DRVI:
IN
STAT
;Get status again
0009
E6 40
ANI
RDA
;Data avail?
000B
CA 0400
JZ
DRVI
;Wait
000E
DB 21
IN
DATA
;Get the char rec'd
0010
E6 7F
ANI
NPAR
;Strip parity, if any
0012
FE 13
CPI
CTLS
;CH/-S?
0014
CA 0400
JZ
DRVI
;Yes, wait till printer ready
0017
FE 11
CPI
CTLQ
;CTL~Q?
0019
C2 0400
JNZ
DRVI
;No, not ready yet
001C
DB 22
DOUT: .
IN
STAT
;Get status
00 IE
E6 80
ANI
TBE
;Port ready for output
0020
CA 1C00
JZ
Dcxn
;No, wait
0023
79
MTV
A,C
;Mcrve char to A-reg
0024
D3 21
an
DATA
; CUtput char to printer
0026
C9
RET
The code
can
easily
be modified
for any senai port by
changing the port addresses and the status bits. The reader
should also note that when the power is off on the WH14,
input data on the serial port will be a 00H. This fact can be
used to print a message on the console device. Also, if one
looks at the status, one will see an overrun condition. This
can be ignored. □
Lachman K. Sippy is currently with the University of
California in a computer planning capacity. He has worked
in (he past for both Boeing Airplane Company and IBM.
He is also the Director of Innovative Interfaces, Inc., a
Berkeley-based company which has pioneered the use of
microcomputers in large libraries.
Page 30
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
425
PROGRAM
DOCUMENTATION
by Freeman L. Moore
Computer programming: is it merely
writing a set of instructions to accomplish
a specific task? I would hope we agree
that writing the set of instructions can
be a very involved process—working
with such things as clarifying the problem
statement, developing an algorithm, flow¬
charting, testing, debugging, documenta¬
tion, and writing the code or instructions.
Quite often, one considers a program com¬
pleted when it produces the correct re¬
sults. This may be acceptable for pro¬
grams which are used only once; but
for production jobs which are kept and
used again, good documentation is essen¬
tial.
Documentation of a computer pro¬
gram should consist of the problem state¬
ment, operating instructions, flowcharts
and sample input and output, among
other items. Some features are part of
what might be referred to as a “user’s
manual,” while others belong to a “pro¬
grammer’s manual.” Ideally these two
manuals will be kept separate since it
should never be assumed that the user is
capable of programming, and that the
programmer tends to forget the needs
of the naive user.
The user’s manual should include
sample input; sample output; anticipated
errors, their meaning and possible correc¬
tions; and, purpose of the program.
Sample input is necessary to provide the
user with an idea of what the program
expects, while the sample output will
reinforce the user’s belief in the pro¬
gram by having results to compare.
Including a directory of errors should
not be considered discouraging to the
user. Such a directory lets a user know
the program is capable of detecting
errors without causing unknown conse-
qences. If an unexplained error message
should appear, then expand upon it in
Freeman L. Moore-Computer Science
Dept., Central Michigan University, Mt.
Pleasant, MI 48859
Page 32
426
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
69
0019
CE
02
08
ERR2
LDX
#MERR2
CAN’T OPEN INPUT FILE
70
001C
20
03
BRA
ERROUT
71
001E
CE
02
23
ERR3
LDX
♦MERR3
CAN’T OPEN OUTPUT FILE
72
0021
BD
05
09
ERROUT
JSR
PSTRNG
73
0024
CE
01
B9
LDX
♦FINAL
PRINT FINAL MESSAGE
74
0027
BD
05
09
JSR
PSTRNG
75
002 A
7E
71
03
JMP
DOS
AND RETURN TO FLEX
76
*
77
* START
PROGRAM BY OPEMI
MG FILES
78
*
79
002D
CE
01
88
XTRl
LDX
♦INTRO
PRINT STARTING MESSAGE
an
0030
BD
05
09
JSR
PSTRNG
81
0033
CE
02
B 8
LDX
#FCBIN
82
0036
an
71
27
JSR
GETFIL
PROCESS FILE SPEC AS INPUT FILE
83
0039
25
D9
BCS
ERR1
SYNTAX ERROR?
84
003B
CE
02
B8
LDX
♦FCBIN
85
003E
86
03
LDA
A
#3
SET EXT FOR .BAS FILES
86
0040
BD
71
2D
JSR
SETEXT
87
0043
C6
09
LDA
B
#9
MUM OF CHARS IN FILENAME
88
0045
FE
02
A5
COPY
LDX
CHAR90
INPUT FILENAME POSITION
89
0048
A6
on
LDA
A
o,x
GET CHAR
90
0 04 A
08
1 NX
91
004B
FF
02
A5
STX
CHAR90
92
004 E
FE
04
F 8
LDX
PTR1
TRANSFER F1L^ NAME
93
0051
A7
00
STA
A
9,X
TO FCBREM
94
0053
08
1 NX
95
0054
FF
04
F 8
STX
PTR1
96
0057
FE
04
FA
LDX
PTR2
TRANFER FILE MAMF
97
005 A
A7
00
STA
A
0,X
TO FCBEXT
98
005C
08
1 NX
99
005D
FF
04
FA
STX
PTR2
100
0060
5A
DEC
B
DECREMENT CHAR COUNT
101
0061
26
E 2
BNE
COPY
REPEAT UNTIL COPIED
102
0063
CE
02
B8
LDX
♦FCBIN
OPEN FILE
103
0066
86
01
LDA
A
♦ READ
FOR READING
104
0068
A7
00
STA
A
0,X
105
006 A
BD
78
06
JSR
FMS
106
Q06D
26
AA
BNE
ERR2
ERROR IN OPEN PROCESS
107
006F
CE
03
78
LDX
♦FCBREM
OPEN REMARK FILE
108
0072
86
02
LDA
A
♦WRITE
FOR WRITING
109
00 74
A 7
00
STA
A
o,x
110
0076
BD
78
06
JSR
FMS
in
0079
26
A3
BNE
ERR3
ERROR RETURN?
112
007B
CE
04
38
LDX
♦FCBEXT
OPEN CODE FILE
113
007E
86
02
LDA
A
♦WRITE
FOR WRITING
114
0080
A7
00
STA
A
0,X
115
0082
BD
78
06
JSR
FMS
116
0085
26
97
BNE
ERR3
ERROR RETURN?
117
*
118
* M A
1 N
P R 0 C E
SSING LOOP
119
*
120
0087
BD
02
83
CONT
JSR
BCHAR
GFT NEXT NON-BLANK CHARACTER
121
008 A
70
02
A4
TST
EOF
OUT-OF-DATA?
122
008D
27
03
BEQ
CONTI
NOT YET
123
00 8 F
7E
01
53
JMP
DONE
YES - TERMINATE LOOP
124
0092
CE
00
03
CONTI
LDX
♦NUMBER
BEGINNING OF STATEMENT
125
0095
C6
01
LDA
B
♦ TRUE
SET TO TRUE
126
0097
D7
11
STA
B
SNEW
127
0099
D 7
12
STA
B
RNEW
TEST FOR STATEMENT #
128
009B
81
30
CONT 2
CMP
A
♦ ’0
LESS THAN ZERO?
129
009D
2D
OC
BLT
NEXT
YES-GET OUT
130
009F
81
39
CMP
A
♦ *9
GREATER THAN NINE?
131
00A1
2 E
08
BGT
NEXT
YES-GET OUT
132
00A3
A7
00
STA
A
0,X
SAVE AS STATEMENT NUMBER
133
00A5
08
1 NX
134
00A6
BD
02
83
JSR
BCHAR
GET NEXT CHAR
135
00A9
20
F0
BRA
C0NT2
REPEAT PROCESS
136
*
137
00AB
6F
00
NEXT
CLR
0,X
CLEAR END-OF-NUMBER
138
00AD
20
03
BRA
TYPE
139
00AF
BD
02
83
TYPEA
JSR
BCHAR
GET CHAR
140
*
141
* MOV/ DETERMINE STATEMENT TYPE
142
143
*
144
00B2
97
0D
TYPE
STA
A
SAVE
SAVE 3-LETTER
145
00B4
BD
02
83
JSR
BCHAR
KEYWORD
146
00B7
97
0E
STA
A
SAVE+1
147
00B9
BD
02
83
JSR
BCHAR
148
00BC
97
OF
STA
A
SAVE+2
149
00BE
C 6
01
LDA
B
n
CONSTANT ONF
150
ooco
96
0D
LDA
A
SAVE
151
00C2
81
52
CMP
A
♦ ’R
TEST FOR R-E-M
152
00C4
26
1C
BNE
STMT
153
00C6
96
0E
LDA
A
SAVE+1
154
00C8
81
45
CMP
A
#’E
155
00CA
26
16
BNE
STMT
156
OOCC
96
OF
LDA
A
SAVE+2
157
00CE
81
4D
CMP
A
#’M
158
00D0
26
10
BNE
STMT
159
00D2
86
01
LDA
A
♦ TRUE
FOUND ONE!
160
00D4
97
10
STA
A
REM
SET REM SWITCH ON (TRUE)
161
00D6
DE
09
LDX
RCOUNT
162
0008
BD
71
30
JSR
ADDBX
INCREMENT REM COUNTER
163
00DB
DF
09
STX
RCOUNT
164
00DD
CE
93
78
LDX
♦FCBREM
SET FILE - |n (continued)
the user’s manual as well as provide some
clues on how to correct the mistake.
The programmer’s manual is directed
towards the maintenance programmer,
one who is consulted when the program
fails to execute correctly, or when
modifications are desired. Items of inter¬
est to the maintenance-programmer are
commented source listing of the program,
flowcharts, data file descriptions and
layouts, and special or unique processing
needs.
Data file specifications and layouts are
crucial if the application is to be modified
to retain additional information, as well
as being an aid if file dumps are taken to
verify the contents of the existing file.
Flowcharts are an area receiving mixed
reactions from progammmers. Some
proponents consider the flowchart essen¬
tial to the documenation package, where¬
as others are content with a well-docu¬
mented listing. Even the form of the flow¬
chart varies from the ANSI version to
the structured version (see Figure 1).
Alternatives to the flowchart are possible,
such as pseudocode, HIPO charts, and
even computer generated flowcharts.
Comments are the English-like state¬
ments included with the language state¬
ments for the programmer’s benefit,
not the computer’s. It appears that all
computer languages have some feature
which allows for comments, such as the
C of * in column one used by
FORTRAN, the REM statement for
BASIC, the — for ADA, etc. If properly
done, comments can provide a great deal
of the documentation needed for a pro¬
gram. For example, it is common practice
to include a header block of comments at
the top of a program describing the
purpose of the program, the author,
date of last revision, etc. Even throughout
the code, segments of comments can be
introduced, thus visually separating por¬
tions of the program into individual units
of code. Comments are intended to en¬
lighten the reader, not duplicate his
knowledge. For example, consider the
following sample assembly statement:
ADD ONE ADD ONE TO THE ACCUM¬
ULATOR
It is obvious from the instruction what is
being done, so that the comment is
wasted. A more meaningful comment
might be the following:
ADD ONE INCREMENT THE CARD
COUNTER
In BASIC, the remark (REM) state¬
ment is used to denote a comment. Most
versons allow multiple statements per
line, separated by a special character,
generally the colon ( : ). With this ability,
it is possible to write a statement and
immediately follow it with a comment,
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 33
427
much like the assembly example shown
earlier.
The problem with remarks in BASIC
is that they generally require memory
space. The common versions of BASIC
for microcomputers are interpreters.
An interpreter normally keeps the source
program in memory and, upon demand,
decodes the statement and executes it.
If a program were heavily commented,
it would occupy considerably more
memory space, as well as slowing down
execution, than a comparable non-
commented version. Thus it is quite easy
to write a large program for a small
machine and not have enough available
memory space to load the program. One
reaction would be to remove the com¬
ments to conserve space. Since this re¬
moves necessary information, it should
not be done. What are the alternatives?
Consider separating the comments out
of the program as done by EXTRACT.
EXTRACT is a program written for
SWTP BASIC running on a M6800
microcomputer using the FLEX operating
system. EXTRACT will accept as its
input a file containing the BASIC pro¬
gram. The output will consist of two
files, one being all of the remarks found,
and the second containing only instruc¬
tions. The file containing just the RE¬
MARKS can be listed on a hard-copy
device and become a permanent part of
the programmer’s documentation. The
file of statements can be used for sub¬
sequent interpretation. Since it contains
no remarks, its memory requirements
will be smaller and execute faster.
EXTRACT is written in M6800
assembly language in order to properly
read a source file. While SWTP BASIC
can read files, string input is separated
by commas, causing problems during
input. Rather than write an assembly
subroutine for a BASIC program, one
language was used. EXTRACT is care¬
fully commented so that one need only
read the comments and understand the
operation of the program. The concept
of segments of code is used by including
blocks of comments to separate the
major portions. The header block in¬
cludes information about the origin and
purpose of the program. The flowchart
can also be consulted for an overview of
the logic.
For non-M6800 users, could this pro¬
gram be modified for another machine?
Conversion of the concept should not be
difficult due to the quality of the com¬
ments and code, as well as minimal
reliance upon the operating system.
For reasons mentioned earlier, a BASIC
implementation would not be practical.
The idea of documentation lacks en¬
thusiastic backers in the computer indus¬
try. Tools such as EXTRACT should be
employed to automate the process as
much as possible, thus encouraging and
furthering the documentation process. □
165
00E0
20
17
BRA
STMT2
CONTINUE
166
00E2
7F
00
10
STMT
CLR
REM
NOT REMARK STATEMENT
167
00E 5
OE
0B
LDX
SCOUNT
168
00E 7
BD
71
30
JSR
ADDBX
INCREMENT STATEMENT COUNTER
169
OOEA
DF
OB
STX
SCOUNT
170
00EC
CE
04
38
LDX
* FCBEXT
SET FILE-10
171
00EF
7D
no
ii
TST
SNEW
FIRST STATEMENT?
172
0OF2
26
05
BNE
STMT2
YES - BRANCH
175
00F4
86
3 A
LDA A
#' :
NO-OUTPUT SEPARATOR
174
00F6
BD
78
06
JSR
FMS
175
*
176
00F9
FF
05
5B
STMT2
STX
FI LEID
SAVE FILE-ID
177
00FC
96
0D
LDA A
SAVE
MOW
178
00FE
BD
05
10
JSR
OUTFIL
OUTPUT THREE CHARACTER
179
0101
96
0E
LDA A
SAVE + 1
KEYWORD
180
0103
BD
05
10
JSR
OUTFIL
181
0106
96
OF
LDA A
SAVE* 2
182
*
183
* COPY
CHARACTERS UNTIL
CR IF REM, ELSE
184
*
ONLY COPY UNTIL
•
FOUND.
185
*
186
0108
BD
05
10
LOOP
JSR
OUTFIL
OUTPUT TO FILE
187
010B
BD
02
7E
JSR
GCHAR
GET AND COPY CHARACTERS
188
010E
81
0D
CMP A
#CR
END-OF-L1NE?
189
0110
26
10
BNE
0VER1
NO-SKIP OVER
190
*
191
• TEST
IF CR IS NEEDED
AT END OF EACH LINE
192
*
193
0112
7D
00
ii
TST
SNEW
STATEMENT NEEDS ONE?
194
0115
26
08
BNE
LOOPIO
NOPE-BRANCH
195
0117
86
0D
LDA A
#CR
YES-OUTPUT CR
196
0119
CE
0 4
38
LDX
#FCBEXT
197
one
BD
78
06
JSR
FMS
198
011 F
7D
00
12
LOOPIO
TST
RNEW
REMARK NEEDS ONE?
199
0122
26
08
BNE
LOOP20
NO-BRANCH
200
0124
86
0D
LDA A
»CR
YES-OUTPUT CR
201
0126
CE
03
78
LDX
fFCBREM
202
0129
BD
78
06
JSR
FMS
203
012C
7E
00
87
LOOP20
JMP
CONT
GET NEXT LINE OF INPUT
204
*
205
• TEST
1 F THE
: IS IN
A
OUOTE FIELD, SUCH AS
206
*
PRINT
' HI : "
207
*
208
012F
7D
00
13
OVER 1
TST
QUOTE
CURRENTLY IN QUOTE FIELD?
209
0132
27
09
BEQ
0VER2
NO-BRANCH
210
0134
81
22
CMP A
#•"
END OF QUOTE FIELD?
211
0136
26
DO
BNE
LOOP
NOPE-GET NEXT CHAR
212
0138
7F
00
13
CLR
QUOTE
YES - CLEAR SWITCH
213
013B
20
CB
BRA
LOOP
AND CONTINUE
214
*
215
013D
81
3A
0VER2
CMP A
# • :
END-OF-STMT?
216
013F
26
08
BNE
0VER3
NO-SKIP
217
0141
7D
00
10
TST
REM
REMARK?
218
0144
26
C2
BNE
LOOP
YES-REPEAT COPY UNTIL CR
219
0146
7E
00
AF
JMP
TYPEA
NO - GET NEXT TYPE
220
0149
81
22
0VER3
CMP A
»•"
START OF QUOTE FIELD?
221
014B
26
BB
BNE
LOOP
NO-GET NEXT CHAR
222
014D
C6
01
LDA B
#TRUF
YES - TURN SWITCH ON
223
014F
D 7
13
STA B
QUOTE
224
0151
70
B5
BRA
LOOP
AMD REPEAT
225
*
226
• END
0 F
R U N
P
ROCESSING
227
*
228
0153
CE
02
B8
DONE
LDX
#FCBIN
CLOSE INPUT FILE
229
0156
BD
02
A8
JSR
FILECL
230
0159
CE
03
78
LDX
fFCBREM
CLOSE REMARK FILE
231
015C
BD
02
A8
JSR
FILECL
232
015F
CE
04
38
LDX
fFCBEXT
CLOSE CODE FILE
233
0162
BD
02
A8
JSR
FILECL
234
*
235
* FILES
CLOSED
, OUTPUT
TOTALS
236
*
237
0165
CE
00
09
D0NE1
LDX
fRCOUNT
REMARK COUNT
238
0168
5F
CLR B
ZERO SUPPRESS
239
0169
BD
71
33
JSR
OUTDEC
240
016C
CE
01
C6
LDX
fMESSl
241
016F
B0
04
FC
JSR
PDATA
242
0172
CE
00
0B
LDX
fSCOUNT
STATEMENT COUNT
243
0175
5F
CLR B
244
0176
BD
71
33
JSR
OUTDEC
245
0179
CE
01
D 8
LDX
f MESS2
246
017C
BD
04
FC
JSR
PDATA
247
017 F
CE
01
B9
LDX
#FINAL
PRINT FINAL MESSAGE
248
0182
BD
05
09
JSR
PSTRNG
249
0185
7E
71
03
JMP
DOS
ALL DONE!!
250
#
251
* MISCELLANEOUS CONSTANTS AND DATA STORAGE
252
*
253
0188
0D
INTRO
FCB
CR, LF
254
018A
45
FCC "Extract REM
's from a BASIC program, version #"
255
01B7
31
FCB
VERNO+'O
,
EOT
256
01B9
45
FINAL
FCC
'End Extract. '
257
01C5
04
FCB
EOT
258
01C6
20
MESSl
FCC
' REMarks
found. '
259
01D5
00
FCB
CR,LF,EOT
260
01D8
20
MESS2
FCC
' statements found.'
Page 34
428
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
261
01EA
0D
CRLF
FCB
CR,LF,EOT
262
01 ED
53
MERR1
FCC
'Syntax
error In file name.'
263
0207
04
FCB
EOT
264
0208
55
MERR2
FCC
'Unab1e
to open 1NPUT file.'
265
0222
04
FCB
EOT
266
0223
55
MERR3
FCC
'Unable
to open .REM or .EXT file.'
267
0244
OD
FCB
CR, LF
268
0246
44
FCC
'Do they already exist?'
269
02 5C
04
FCB
EOT
270
0250
55
MERR4
FCC
' Unab1e
to properly close a file.'
271
027D
04
FCB
EOT
272
*
273
* SUBROUTINE
TO RETURN
NEXT CHARACTER
274
*
275
* ENTRY
GCHAR
RETURNS
NEXT CHAR WHEREAS ENTRY
276
*
BCHAR
RETURNS
'JFXT MON-BLANK CHAR
277
*
278
027E
7C
02
A7
GCHAR
INC
BFLAG
SET BLANK TRUE
279
0281
20
03
BRA
GCHARl
280
0283
7F
02
A7
BCHAR
CLR
BFLAG
ELSE FLAG FALSE
281
0286
FF
02
A5
GCHARl
STX
CHARQ0
SAVE XR
282
0289
CE
02
B 8
LDX
# F C B 1 N
283
028C
BD
78
06
GCHAR2
JSR
FMS
GET CHAR
284
0 2 8 F
26
0D
BNE
GCHAR8
ERROR RETURN
285
0291
7D
02
A7
TST
BFLAG
TEST BLANK FLAG
286
0294
26
04
BNE
GCHAR3
OK-RETURN
287
0296
81
20
CMP
A
# '
IS IT SPACE?
288
0298
27
F2
BEO
GCHAR2
YES - GET NEXT CHAR
289
029A
FE
02
A5
GCHAR3
LDX
CHAR90
RESTORE XR
290
029D
39
RTS
AND RETURN
291
029E
86
01
GCHAR8
LDA
A
#TRUE
SET
292
02A0
B 7
02
A4
STA
A
EOF
END-OF-FILE ON
293
02A3
39
RTS
294
*
295
02A4
00
EOF
FCB
0
296
02A5
02
BB
CHAR90
FDB
FCBIN+3
XR STORAGE
297
02A7
00
BFLAG
FCB
0
RETURN BLANK INDICATOR
298
*
299
* SUBROUTINE
TO CLOSE
A FILE
300
*
301
02A8
86
04
FILECL
LDA
A
♦ CLOSE
CLOSE CODE
302
0 2 AA
A7
00
STA
A
o,x
303
02 AC
BD
78
06
JSR
FMS
304
02 AF
26
01
BNE
FILER
ERROR?
305
02B1
39
RTS
NO-RETURN
306
02B2
CE
02
50
FILER
LDX
#MFRR4
307
92B5
7E
00
21
JMP
ERROIIT
ERROR PROCESSING
308
*
309
* FILE
CONTROL BLOCKS
(FCB) FOR
310
* . BAS
- INPUT
FILE
311
* .EXT
- CODE FILE
312
* .REM
- REMARK
FILE
313
*
314
02B8
FCBIN
RMB
142
315
0378
FCBREM
RMB
12
316
0384
52
FCC
1 REM'
317
0387
RMB
177
318
0438
FCBEXT
RMB
12
319
0444
45
FCC
'EXT'
320
0447
RMB
177
321
04F8
03
7B
PTRl
FDB
FCBREM+3 FILE NAME PTR
322
04FA
04
3B
PTR2
FDB
FCBEXT+3 FILE NAME PTR
323
*
324
« SUBROUTINE
TO OUTPUT
CHARACTERS,
325
* TERMINATED
3Y EOT.
326
*
327
04FC
A6
00
POATA
LDA
A
0,X
GET CHAR
328
04FE
81
04
CMP
A
♦ EOT
END-OF-STRING?
329
0500
27
06
BEQ
PDATA1
YES - RETURN
330
0502
BD
71
12
JSR
PtlTCHR
OUTPUT CHARACTER
331
0505
08
1 NX
532
0506
20
F 4
BRA
PDATA
AMD REPEAT
333
0508
39
PDATA1
RTS
RETURN
334
*
335
* SUBROUTINE
PSTRNG
336
* CALL PDATM, AND
THEN PRINT CR/LF
337
*
338
0509
8D
FI
PSTRNG
BSR
PDATA
OUTPUT STRING
339
050B
CE
01
EA
LDX
#CRLF
340
050E
20
EC
BRA
PDATA
OUTPUT CR, LF
341
*
342
* SUBROUTINE
OUTFIL -
343
* OUTPUT
ACC-A TO PROPER FILE.
344
* OPTIONALLY OUTPUT
STATEMENT NUMBER 1 F
345
* NEEDED.
346
*
347
0510
B7
05
58
OUTFIL
STA
A
TCHAR
SAVE CHARACTER
348
0513
70
00
10
TST
REM
IN REMARK?
349
0516
26
0A
BNE
OUT 10
YES - BRANCH
350
0518
7D
00
11
TST
SNEW
STATEMENT NEEDS NUMBER?
351
051B
27
2C
BEO.
OUT80
NO-BRANCH
352
051D
7F
00
11
CLR
SNEW
CLEAR INDICATOR
353
0520
20
08
BRA
OUT 50
BR TO OUTPUT STMT #
354
0522
7D
00
12
OUT 10
TST
RNEW
REMARK NEEDS NUMBER?
355
0525
27
22
BEQ
OUT80
NO-BRANCH
356
0527
7F
00
12
CLR
RNEW
CLEAR indicator (continued)
Figure 1.
Structured Flowchart for EXTRACT
open input file (.BAS)
open output file (.REM)
open output file (.EXT)
loop until end-of-input-file
save statement number
loop until end-of-line
type = 'REM'
increment
remark
counter
increment
statement
counter
: needed
output
to
file
loop until : or EOL
get character
output to proper
file
print counts of statements
and remarks
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 35
429
357
*
358
* OUTPUT
STATEMENT NUMBER
359
*
360
05 2 A
CE
00
03
OUT50
LDX
♦NUMBER
361
052D
FF
05
59
STX
SAVEXR
PT TO FIRST DIGIT
362
0530
FE
05
59
OUT60
LDX
SAVEXR
363
0533
A6
00
LDA
A
0,X
GET DIGIT
364
0535
27
12
BEQ
OUT80
BR IF MO MORE
365
0537
08
1 NX
ADVANCE TO NEXT DIGIT
366
0538
FF
05
59
STX
SAVEXR
AND SAVE POSITION
367
053B
FE
05
5B
LDX
FILEID
368
053E
BD
78
06
JSR
FMS
OUTPUT TO FILE
369
0541
27
ED
BEQ
OUT 60
REPEAT IF NO ERROR
370
0543
CE
05
5D
OUT65
LDX
#I0ERR
371
0546
7E
00
21
JMP
ERROUT
ERROR PROCESSING
372
*
373
* OUTPUT
' SINGLE
: CHARACTER
1 (TCHAR)
374
*
375
0549
FE
05
5B
OUT80
LDX
FILEID
376
054C
B6
05
58
LDA
A
TCHAR
OUTPUT CHARACTER
377
054F
BD
78
06
JSR
FMS
378
0552
26
EF
BNE
OUT65
ERROR?
379
0554
B6
05
58
LDA
A
TCHAR
RESTORE CHAR
380
0557
39
RTS
AND RETURN
381
*
382
0558
00
TCHAR
FCB
0
STORAGE FOR SINGLE CHAR
383
0559
00
00
SAVEXR
FDB
0
XR STORAGE
384
055B
00
00
FILEID
FDB
0
ADDRESS OF FILE-FCB
385
05 50
49
I0ERR
FCC
'1/O error
when writing to output
386
0583
04
FCB
EOT
387
END
XTRACT
NO ERROR(S)
DETECTED
♦♦♦EXTRACT,SIMPLE.BAS
Extract REM's from a BASIC program, version #1
3 REMarks found.
4 statements found.
End Extract.
♦♦♦LIST,SIMPLE.EXT
20LET A=5
30PRINT A :PR I NT "MULTIPLE STATEMENTS"
50END
♦♦♦LIST,SIMPLE.REM
10REM THIS IS A REMARK
20REM THIS IS AN INLINE REMARK
40REM ALL DONE
♦♦♦LIST,SIMPLE.BAS
10 REM THIS IS A REMARK
20 LET A-5 : REM THIS IS AN INLINE REMARK
30 PRINT A : PRINT "MULTIPLE STATEMENTS"
40 REM ALL DONE
end
Symbol Table
ADDBX
7130
BCHAR
0283
BFLAG
02A7
CHAR90
02A5
CLOSE
0004
CONT
0087
CONTI
0092
CONT2
0098
COPY
0045
CR
0000
CRLF
01EA
DONE
0153
DOME 1
0165
DOS
7103
EOF
02A4
EOT
0004
ERR1
0014
ERR2
0019
ERR3
001E
ERROUT
0021
FCBEXT
0438
FCB 1 N
02B8
FCBREM
0378
FILECL
02A8
FILEID
055B
FILER
02B2
FINAL
01B9
FMS
7806
GCHAR
027E
GCHAR1
0286
GCHAR2
028C
GCHAR3
029A
GCHAR8
029E
GETFIL
7127
INTRO
0188
I0ERR
055D
LF
000A
LOOP
0108
LOOPIO
011F
LOOP20
012C
MERR1
01ED
MERR2
0208
MERR3
0223
MERR4
025D
MESS1
01C6
MESS2
01D8
NEXT
00AB
NUMBER
0003
OUT10
0522
OUT 50
052A
OUT60
0530
OUT 6 5
0543
OUT 80
0549
OUTDEC
7133
OUTFIL
0510
0VER1
012F
0VER2
013D
0VER3
0149
PDATA
04FC
PDATA1
0508
PSTRNG
0509
PTR1
04F8
PTR2
04FA
PUTCHR
7112
QUOTE
0013
RCOUNT
0009
READ
0001
REM
0010
RNEW
0012
SAVE
000D
SAVEXR
0559
SC0UNT
OOOB
SETEXT
712D
SNEW
0011
STMT
00E2
STMT2
00F9
TCHAR
0558
TRUE
0001
TYPE
OOB2
TYPEA
00AF
VERNO
0001
WRITE
0002
XTR1
002D
XTRACT
0000
(continued from page 9)
NLOGS cont’d
NOTE
Following the terminology well-
established by the pocket calculator,
the following abbreviations will be
used in the balance of this paper: LOG
will stand for “the logarithm to the
base 10;” EXP will mean “10 raised to
the _ power.” The distinction be¬
tween LOG (logjp) and log (general
term) should be kept in mind.
REFERENCES
Reference (1): The article on “Loga¬
rithms” in the 1967 edition of the
Encyclopaedia Brittanica, by K.O.
May.
Reference (2): The International Dic¬
tionary of Applied Mathematics;
D. Van Nostrand 1960; definition
of “A ccuracy. ”
Reference (3): Keneth A. Simons,
“The dB Anything,” Proc. IEEE
(Letters), pp. 495-96, April 1973.
Page 36
430
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
MCVIT
by William D. Loughman
The standard 2000 hex address of the North-Star DOS can
be an annoyance at times. Large programs starting anywhere
below the DOS sometimes cannot be loaded from disk, as the
DOS may be overwritten before the load is completed. There
are a lot of nice programs which were not designed for use
with the N * disk system.
These can be used painlessly by tacking them onto a short
‘mover’ program. MOVIT cares not where it is started. It
finds its own location in RAM by putting a ‘RET’ at 0 hex,
executing ‘RST O’, and accessing the stack to find the return
address. Subsequent operations are all by adding offsets to
this reference address. MOVIT is short enough to enter ‘by
hand’ with a monitor; just pay attention to changes needed
in lines 80-81 and line 93. If you use an assembler, in addi¬
tion to those changes you should delete line 16 and you must
change the execution address assignment in line 41. After
assembly, load your own program to reside at whatever ad¬
dress is represented by line 100. The 6 bytes there are only a
sample; load on top of them. Save the combined programs to
disk.
Now the combination can be loaded from disk and execu¬
ted at almost any arbitrary location in memory. Your pro¬
gram will be moved to its correct location (overwriting the
DOS, perhaps) and started up. I give my disk files a ‘GO’
address in high memory, making sure the loaded program will
fit. Then all I need to do is ‘GO .. .’, and it auto-executes
just like ‘proper’ programs do.
An aside: this letter is formatted using H. Watson’s POW
(DDJ #29). L. Morgenstem modified that for use with Pro¬
cessor Tech’s EDIT program (DDJ #32:42 Feb. 70). I have
adapted the latter version for use with either ALS-8 or PILOT
file structures, which I use in my home-brew (disk) operating
system. This allows use of the nice screen editors in those
programs, and thus provides a pretty good and very, very in¬
expensive CRT word processor system. Many thanks to them,
and to you. O
LISTING
ASSMX 0
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0001 * * MOVIT *
0002 *
0003 * An address-independent routine for
0004 * 'load-and-go' use, from disk, of
0005 * programs blocked by the standard
0006 * NorthStar DOS at 2000 hex.
0007 *
0008 * Orig. : Wm.D.Lougliman 1 May 1980
0009 * PUBLIC DOMAIN: 12 June 1980
0010 *
0011 * Set BYTES, BOTAD, and XEQ (below)
0012 * to reflect your own program needs.
0013 * (EXAMPLES below: use for a test)
0014 *
0015 * my OS and assembler usage:
0016 SOLOS EQU 0C004H for EXAMPLE
0017 SP EQU 6 (for ALS-8)
0018 *
0019 * Assemble this program-mover at any
0020 * convenient address. Add your own
0021 * program to it at PROGM (below).
0022 *
0023 * Create a disk file large enough to
0024 * hold BOTH your program AND this
William D. Loughman -293 Gravatt Dr., Berkeley, CA 94705
0000
0025
*
preamble.
Save all of it to disk.
0000
0026
*
0000
0027
*
Give
the disk file
any convenient
0000
0020
*
'GO'
address which
is neither in
0000
0029
*
the :
DOS address space, nor that of
0000
0030
*
your
program's final location.
0000
0031
*
0000
0032
*
Now,
•GO
(filename)', and enjoy.
0000
0033
*
0000
0034
*
0000
0035
*
—
- SET
VARIABLES HERE —
0000
0036
*
your
program's length in bytes:
0000
0037
BYTES
EQU
6
for EXAMPLE
0000
0038
*
your
program's correct load addr:
0000
0039
BOTAD
EQU
0
for EXAMPLE
0000
0040
*
your
program's execution addr:
0000
0041
XEQ
EQU
SOLOS
for EXAMPLE
0000
0042
*
0000
0043
*
0000
0044
*
—
MOVIT —
0000
0045
*
assume a valid stack (1 call);
0000
0046
*
and
find our own RFRNC address
0000
21
00
00
0047
LX I
H, 0
'RST 0' needs
0003
36
C9
0048
MV I
M, 0C9H
'RET'
0005
0049
*
0005
C7
0050
RST
0
call it
0006
3B
0051
PFRNC
DCX
SP
return here
0007
3B
0052
DCX
SP
to get
0008
E3
0053
XTHL
.
RFRNC addr
0009
5P
0054
MOV
E,L
clone it
000A
54
0055
MOV
D, H
00 0B
0056
*
now,
make
our own
stack at RFRNC,
00 0B
0057
*
ruining this nice
program*
000B
F9
0053
SPHL
oooc
0059
*
oooc
0060
*
find
MOVE
addr
oooc
3E
20
0061
MV I
A,MOVE
-RFRNC offset
000E
85
0062
ADD
L
plus RFRNC addr
000F
6F
0063
MOV
L, A
0010
3E
00
0064
MV I
A , 0
0012
8C
0065
ADC
H
0013
67
0066
MOV
II, A
is MOVE addr
0014
E3
0067
XTHL
.
saved in stack
0015
0068
*
0015
0069
*
find
PROGM (to move)
0015
EB
0070
XCHG
.
REFRNC addr
0016
3E
2D
0071
MV I
A,PROGM-RFRNC
0018
95
0072
ADD
L
plus offset
0019
6F
0073
MOV
L, A
001A
3E
00
0074
MVI
A, 0
001C
R C
0075
ADC
H
ooin
67
0076
MOV
H , A
001E
ER
0077
XCHG
is PROGM addr
001F
0078
*
001F
0079
*
set
up the move
001F
01
06
00
0030
LXI
B,BYTES its length
0022
21
00
00
0081
LX I
H,BOTAD its load addr
0025
F.3
0032
XTHL
.
(balances MOVE)
0026
0083
*
0026
0034
*
move
the
program;
execute it
0026
E3
0085
MOVE
XTHL
.
get load addr
0027
1A
0086
LDAX
D
move a byte
0028
77
0087
MOV
M,A
0029
13
0083
INX
D
set up next
002A
23
0089
INX
H
002B
0B
0090
DCX
B
bytes-1
002C
79
0091
MOV
A ,C
002D
B0
0092
ORA
B
done?
002E
CA
04
CO
0093
JZ
XEQ
do it, else
0031
0094
*
put
load .
addr in stack, also
0031
E3
0095
XTHL
.
get MOVE addr
0032
E9
0096
PC1IL
.
and do more
0033
0097
*
0033
0098
*
your
program goes
here,
0033
0099
*
replacing
this dummy.
0033
0100
PROGM
EQU
$
0033
11
n
0101
DW
1111H
003 5
2 2
2 2
0102
DW
2222H
0037
33
33
0103
DW
3333H
0039
0104
*
BOTAD
0000
0081
BYTES
0006
0030
MOVE
0026
0061
PROGM
0033
0071
RFRNC
0006
0061
0071
SOLOS
C004
SP
0006
0051
0052
XEQ
C004
0093
€ND
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 37
431
6800 and 1802
Cross-Assembler for CP/M
by William C. Colley III
What Is a Cross-assembler?
A cross-assembler, like a normal assembler, is a program
that converts human-readable assembler source code for a
given microprocessor into binary machine code for the same
processor. The difference between a cross-assembler and a
normal assembler is this: a normal assembler program is
run on the same type of processor as the output of the assem¬
bler and a cross-assembler program is run by a different pro¬
cessor. For example, a 6800 assembler runs on a 6800 and
converts source code in 6800 machine code. This particular
6800 cross-assembler runs on an 8080 or Z-80 and converts
6800 source code into 6800 machine code.
With an appropriate cross-assembler, you can write and
assemble code for another (in this case 6800 or 1802) pro¬
cessor using your existing (in this case CP/M) editors and
floppy disks. This keeps you from having to have separate
disks, disk operating systems, editors, etc. for each different
processor.
General Description of Both Cross-assemblers
CP/M comes with an assembler (ASM.COM) of about the
same capabilities as these two cross-assemblers. Thus, the
cross-assemblers will be described in terms of how they
compare to the ASM.
The assembler syntax of the cross-assemblers is similar to
ASM’s, but not identical. Line numbers are not permitted, as
the cross-assemblers make no attempt to scan them off. A
leading * will cause an error rather than mark a comment line.
Comment lines should begin with a semicolon. No colons
should appear after labels as the colon is a legal alphabetic
character and will become part of the symbol name. Labels are
distinguished from opcodes by the fact that labels begin in
column 1 and opcodes do not.
The opcodes are those of the particular microprocessor
instead of those of the 8080. The only lower-case to upper¬
case conversions performed by the assembler are in opcocdes
and keywords such as NOT, AND, MOD, etc. Thus the opcode
“LDA” is the same as “Ida”, but the label “LABEL” is not the
same as the label “label”.
The expression evaluator has more operators than ASM’s
and the operators have a slightly different precedence order.
The additional operators are:
HIGH meaning “the high byte of”
LOW meaning “the low byte of”
relational operators EQ, NE, LT, LE, GT, GE (which can also be
written as =, O, <,<=,>, >= respectively)
William C. Colley, III-409 Marlborough St. #24, Boston
MA 02115
Finally, the pseudo-ops have been renamed according to
the particular processor. Also the IF-ENDIF pair has been
enhanced to IF-ELSE-ENDI. The ELSE is, of course, optional.
Like ASM, the output of the cross-assemblers is in INTEL
hex. This was chosen because INTEL hex can be loaded into
memory by DDT and SID. Of course, the disassembly functions
of DDT and SID will not work correctly on a non-8080
instruction set.
Particular Description of the 6800 Cross-assembler
The 6800 cross-assembler’s basic syntax is as follows:
[label] LDA A X, 3 Comment field.
The parser is built such that the accumulator specifier “A”,
the indexed mode designator “X”, and the offset “3” can be
specified in any order. The designators “A”, “B”, and “X”
can be written in either upper or lower case. Immediate
addressing is specified by a #sign as per Motorola usage.
Also in accordance with Motorola usage, two formats for
numeric constant are supported. The Motorola-format con¬
stant $FF is equivalent to the INTEL-format constant 0FFH.
Hex numbers and INTEL-format base designators can be
written in either upper or lower case.
The current location counter is referenced by a * instead of
the $ sign as per Motorola usage.
Finally, when given the choice between direct (short)
addressing and extended (long) addressing, the assembler will
choose direct addressing if the following two conditions are
met:
1. The address in question contains no forward references.
2. The address in question is in the range 0 to $FF.
Particular Description of the 1802 Cross-assembler.
The 1802 cross-assembler implements two additional
pseudo-ops above the set available in ASM. They are:
1. PAGE which sets the current location counter to the top of the
next 256-byte page, and
2. LOAD register, value
This is, in effect, a built-in macro. The assembly of a
LOAD pseudo-op places the following code into the object
file:
LDI HIGH value
PHI register
LDI LOW value
PLO register
The LOAD pseudo-op is included since this construct is so
Page 38
432
Dr. Dobb's Journal of Computer Calisthenics 8i Orthodontia
Number 50
common in 1802 code that RCA saw fit to include it as a
pseudo-op in some of their assemblers
What Machine Resources are Required?
The cross-assemblers are supplied in source form only
(except as noted below) as both the source and object of the
assemblers would not fit on a single-density 8” disk with the
other three programs on the disk. Each assembler has six
modules written in BDS C. A seventh module (called either
A68TBLS. MAC or A18TBLS.MAC) is written in Microsoft’s
MACRO-80 in such a way that it assembles into a link module
for the BDS C linker. The details as to how this is done are
included on the disk. In addition, for those who have BDS C
but not MACRO-80, the assembled versions (A68TBLS.
CRL and A18TBLS.CRL) are included on the disk. BDS C
and MACRO-80 are available through Lifeboat Associates
who advertise in most of the microcomputer magazines.
The required machine resources are thus:
1. the BDS C compiler, and (optionally) the MACRO-80 macro¬
assembler,
2. 40K or more of RAM, and
3. CP/M version 1.3 or 1.4.
The cross-assemblers have not been tested under CP/M 2.x,
though there should be no problems involved.
What Do I Get and Where Do I Get It?
The cross-assemblers are available on single-density 8”
disk from the C User’s Group. Send them a disk and enough
postage to mail it back to you. Write to: C User’s Group,
c/o John Nall, Computer Center, Love Building, Florida
State University, Tallahassee, Florida, 32306, (904) 644-
2764.
The disk includes the 8 source files of each cross-assembler
(an include file, 6 C modules, and the MACRO-80 module),
the assembled versions of the MACRO-80 modules, and print
image copies (ready to pip to 1st:) of the 20-page user
manuals. The disk also includes a combination BDS
C/MACRO-80 program that uses a parallel input bit and a
parallel output bit to read and write cassette tapes compatible
with the El.F II. This gives you a method of getting the
output of the 1802 cross-assembler into an 1802 system to be
executed. The tape program also requires a simple hardware
interface (1 CMOS chip, 5 resistors, 2 capacitors, and a po¬
tentiometer) that is diagrammed in the program documenta¬
tion. A couple of useful disk utilities written in BDS C are also
on the disk.
Conclusion
I wrote the cross-assemblers for my own use and for the
use of a friend. I saw no reason, however, why others should
have to “reinvent the wheel,” so I am trying to distribute them
to anyone who wants them. I hope they prove useful, o
A legal note: CP/M, ASM. DDT, and SID are trademarks of Digital Re¬
search, and MACRO-80 is a trademark of Microsoft.
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 39
433
1
wm mm
nr
■
■
■
>P0f
90S!
9l On Strings f
by Ralph Deane
on 1
FOR
th]
1
1
__ 1
\— _
_
=:::=!
Once a person has used FORTH
for a period of time, two deficiencies
usually appear. These are the lack of
floating point (real) numbers, and the ab¬
sence of any string handling functions.
Much of the work currently being done in
BASIC could be done quicker and easier
in FORTH if these two problem areas
were fixed.
The area of floating point numbers
has been adddressed by different groups,
and Kitt Peak Observatory has published
their approach in the Kitt Peak FORTH
Primer. This will probably become the
standard in the future.
The problem of string handling in
FORTH is an area which, as yet, has
received little attention. In this article
I propose to outline one approach to
solving this problem. In no way is this
method to be thought of as a finalized
standard solution to string handling.
It is meant to be a starting point from
which to build a unique (and powerful)
string handling package.
The obvious place to start is at the
beginning: creating string variables. Since
FORTH is a member of the structured
family of languages, it requires all vari¬
ables to be declared before use. String
variables will be no exception. This raises
the first problem: should we allow
strings to have unlimited length or should
they have a maximum length set by the
system? Also, where shall we store the
string data: in the dictionary or in a
separate table?
In order to remain compatible with
the other data types supported by the
language, I feel that the string should be
stored in the dictionary. This gives the
user maximum access to the data with a
minimum of overhead. This storage
system will also require that a maximum
length be set by the system in order to
know where the next free dictionary
location is situated. If the maximum
length is set at 255 (the same as Micro-
Soft BASIC) then any character in the
string can be addressed with an eight
bit index register. This can be very
Ralph Deane-Box 27, Little Fort, BC,
Canada VOE 2C0
important on most micros in terms of
speed and program size.
Another nice feature would be to
allow the user to specify, for any string
variable, a maximum length which is less
than or equal to the system’s maximum
length. This would allow a great saving
in dictionary space requirements for
short strings. It hardly makes sense to
reserve 255 bytes of space for a variable
which the user knows will have a maxi¬
mum of 10 characters stored in it.
If the user is allowed to specify a
maximum size, then that size should
be stored at the start of the string area. A
null ($00) should also be stored as the
last character in order to signal the end
of the string. This would give an over¬
head of two bytes per variable but would
make for much more efficient program¬
ming.
In keeping in line with other FORTH
variables, a string variable should place
the address of its first character on the
sack when the variable name is executed.
It should also put the current length of
the string on the stack. The reason for
this is that the current length can vary
from the maximum length and the string
handling functions should not have to
search a string in order to know its length.
This would also make it compatible with
the string output function, TYPE, which
has already been defined. Since TYPE
requires the length to be the top stack
value, with the address second, let’s also
define string variables so that they place
their data on the stack in the same order.
Now that we have defined the form
of our string variables we only need to
implement them via a variable defining
function.
The defining function could be called
STRING (a rather obvious choice)
and will probably be defined by using
< BUILDS and DOESX FIGURE I
shows two different approaches to im¬
plementing STRING. Function (a) creates
a variable whose current length is equal
to the maximum length and which
contains all blanks. Function (b) will
create string variables with a current length
of 1, with that character being a blank.
Neither (a) nor (b) will allow variables
to be created with a maximum length
less than 1 or greater than 255. The
runtime routine of both (a) and (b)
are identical. It increments the starting
address of the character string around
the length byte and then searches the
string to find the current length. This
data is left on the stack in the required
order.
The other data type associated with
strings, besides variables, is the literal
string. This is usually a string of char¬
acters enclosed in quotes. Since the single
quote, ’, has already been used as a func-
FIGURE I
o
i
9
3
4
5
A
7
6
9
10
:l :l
1.2
1.3
1.4
tapes )
1. + SWAP 0= END SWAP
DECIMAL
( Definition of STRING - two
{ SRCH DUP BEGIN DUP C@ SWAP
( Type a STRING definition )
5 STRING <BUILDS ABS 255 MIN 1. MAX DUP Cv 0 DO 32 C
LOOP 0 C» D0ES> 1 + DUP SRCH i
< Type b STRING definition >
! STRING <BUILDS ABS 255 MIN
0 Cv LOOP D0ES> 1 + DUP SRCH i
< When definin'? STRING you must chose either type a
or type b to implement. See text for an explaination
of the differences. >
1
DECIMAL
MAX DUP
Cv 32 Cv 0 DO
Page 40
434
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
tion name we will have to use the double
quote, ”, Since ” will be used as a
function name it must be separated
from the rest of the strings by a blank.
Another ” can be used as the termi¬
nating character.
Since we desire maximum flexibility
from any function, the literal string
function must be directly executable or
compilable, depending on the user’s
needs. It should also be compatible with
the string variables so that the string
handling functions do not have to know
which data type they are dealing with.
This means that a literal string, when
executed, will place the starting address
of the data, as well as the string length,
on the stack. The string, wherever it is
stored, must also have a null ($00)
appended to it to signify the last char¬
acter.
An inspection of FIG FORTH’S .”
function shows a method which can be
used to define the ” function. The
function is split into two parts and the
compilation flag is used to choose which
part is executed. If ” is being used inside
a colon definition (i.e., :the flag is set)
the string is compiled into the dictionary
along with the address of a runtime
routine, (”), and the string length.
The function ( ” ), when executed, will
place the string address and its length
on the stack.
Direct execution of ” produces a dif¬
ferent sequence. The string is stored in
the area at the end of the dictionary,
along with its length and terminating
character. The address of this area and
the length of the string is then placed on
the stack. Since the string is stored in a
rather volatile area, any operations to be
performed on it must be done before
anything else is added to the dictionary.
The definition of ” is left up to the
implementor as it will depend on the
specific system being used. The
function can be used as a model if so
desired. One thing to be remembered
is that a null must be appended to the
string for proper operation of the hand¬
ling functions. Also ” is to be made an
immediate function.
Now that the format and runtime
characteristics of the string data types
have been outlined we can go on and
define some string handling functions. At
the minimum the package should contain
all the string functions supported by
BASIC. More functions can be added as
the need arises.
One of the first functions needed is
the string store routine. In keeping with
a FORTH standard it will be called
S! (pronounced string-store). It will
take data from one string and place it
in another. The variable in which the
data is stored will have a null placed at
the end of the new string to indicate the
current length. The string will also be
truncated if its length is longer than the
variable’s maximum length.
Where S! is used to replace the whole
string, the function SUB! is used to re¬
place a substring on a one-for-one
basis. The current length of the variable
will be unchanged by use of SUB! . If the
string is longer than the substring it
replaces, it will be truncated at the
substring’s length.
The stack values required for S! and
for SUB! are identical. The top two
values are the address and length of the
destination string (or substring). The
next two values are the address and
length of the source string. The lengths
do not have to match, as the string is
adjusted to fit the destination string.
FIGURE II is one method of defining
S! and SUB! . Trying to store into a
literal string, while possible, is a real
no-no and drastic happenings can occur if
it is attempted.
The next type of handling function to
be discussed will be the substring ex¬
traction routines. These include MID$,
LEFT, and RIGHTS. These functions
generate addresses and lengths of speci¬
fied substrings. Since LEFTS and RIGHTS
are just special cases of MIDS, we will
concentrate on it for the moment.
There are two different types of
MIDS functions presently in use in
BASIC. One type requires the starting
character location and the length of the
desired substring. The other needs the
location of both the starting and ending
characters.
I have, for no specific reason, chosen
the second type of MIDS. The first type
can be used if so desired, and is equally
as easy to define. MIDS should make
sure that the substring it defines is
entirely inside the parent string. If it is
not, then the starting and ending loca¬
tions should be adjusted. MIDS expects
the top two stack values to be the address
and length of the parent string. The next
value is the ending character location,
while the last value is the starting char¬
acter location. These last two values will
be forced into the range of 1 to the cur¬
rent string length. MIDS will return the
address and length of the substring as
defined by these values.
LEFTS is the special case of MIDS
where the starting character location is
assumed to be 1. Only the address and
length of the parent string, as well as the
ending character location, are needed.
RIGHTS is another special case in which
the ending character location is assumed
to be the last character in the parent
string. The starting character location
and the parent string information is all
that RIGHTS requires. FIGURE III
is one possible definition of MIDS,
RIGHT and LEFTS.
Concatenation of strings is another
P
FIGURE II
0 ( Definition of S! and SUB! )
1 : S' DROP DUP t - CP ROT MIN 1 MAX OVER OVER +
2 0 SWAP C- CMOVE f
3
4 ! SUB! ROT MIN 1 MAX CMOVE f
5
6 ( Note that in PIG FORTH the function C- is called C! )
7
B
o
10
11
I 2
1.3
14
1. 5
FIGURE III
0 ( Definitions of MIDS. LEFTS and RIGHTS )
1 : MIDS SWAP SAVE ROT MIN 1 MAX SWAP OVER MAX OVER
2 + SWAP UNSAVE + 1 ~ SWAP OVER SRCH MIN 5
3
4 : LEFTS SAVE SAVE 1 SWAP UNSAVE UNSAVE MIDS -S
5
6 ! RIGHTS SAVE SAVE 256 UNSAVE UNSAVE MIDS i
~\
L.L
8 ( Note that in FIGFORTH the functions SAVE
9 are called >R and R> » respectively* )
10
11
12
13
14
15
is rid UNSAVE
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 41
435
function which should be part of the The implementor can tailor these func- lists the definitions for SINP and S =
package. S + will be used as the conca- tions to each individual system. FIGURE This concludes my proposal for string
tenation function name. Due to the way V shows the definitions for LEN and handling functions for FORTH. I have
that strings have been defined S + will MLEN. tried to present a string data type which
have a few restrictions. The location Two more functions which might be will be easy to add new functions to at
literal strings are stored in, when di- useful to have in the package are string a later date. This is very important in
rectly executed, rules out their being input (SINP) and string comparison FORTH as the language is so easily ex-
both arguments of S +. Also the resulting ( S= ). SINP expects the top two stack tended that new functions are con¬
string produced by S + will have a maxi- entries to describe the string into which stantly being added. In order to show the
mum length of 255, as no variable can the input data is to be placed. This should power of these functions I have recoded
hold more characters than that. S + be a variable. S= assumes the top four the Soundex program which was present-
will store the new string in a temporary stack entries describe the two strings ed in the MAY 1980 issue of BYTE
location ana place that address and string which are to be compared. It will return magazine on pages 196-200. Executing
length on the stack. A null will be ap- a 1 if the strings are identical, including SOUND will cause a prompt for the
pended to the new string. length, and a 0 otherwise. FIGURE VI name. The name is terminated after 30
Since one of the arguments of S +
can be a literal string, we cannot use
the area at the end of the dictionary as
temporary storage. An argument could
be destroyed if we did. Instead we
will have to create a storage area in the
dictionary. This could be done with an
ARRAY definition or any other storage
reserving method. If the ARRAY data
type is supported on the system, it is the
easiest way to reserve space and still
have access to the address. The temporary
storage area must be 256 bytes (255
characters plus a null) long. FIGURE IV
shows one possible definition of S +.
Assume that the top two stack values
define a string called B, while the next
two values define the string A. S +
will produce the string (A + B). This new
string will be truncated after 255 char¬
acters, with the first data coming from
string A.
A few miscellaneous functions are
all that is needed to complete the basis
of our string handling package. These
include VAL, STR$, LEN and MLEN.
We shall now look at these individually.
VAL is used to convert the string
representation of a number into its
numeric value. In FORTH this should
be done with regard to the current
BASE. When VAL is executed, the top
two stack values describe the string to
be converted. Conversion will stop
at the first non-numeric character. The
value computed is left on the top of the
stack.
STR$ converts a number into a string
representation of that number. This
should also be done with regard to the
current BASE. The top stack value is the
number to be converted. STR$ will leave
the address and length of the string
produced on the stack. A special area can
be set aside to hold the string or it could
be treated as a literal string. A null should
be appended to the end of the string.
Since precision numbers would require
a maximum of 7 characters of storage.
LEN returns the current length of the
string defined by the top two stack
entries. MLEN returns the maximum
length of that string.
Since VAL and STR$ can make good
use of routines already a part of the sys¬
tem, no definitions are shown for them.
Page 42
436
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
characters or a carriage return. The the code produced. For more information
Soundex code is then computed and on Soundex codes consult the BYTE
typed out. The string variable S$ contains article. □
FIGURE VII
Soundex Coder
0 ( DEFINITION OF SOUNDEX CODER )
1 DECIMAL
2 30 STRING N* 1 STRING K* 1 STRING L* 4 STRING S*
3 ! NAME C LAST NAME? I TYPE N* SINP 5
A i FIRST 1 N* LEFT* S* S! i
5 ! ITH I I N* MID* DROP C@ 64 - f
6 i KTH DUP “ 01230120022455012623010202* MID* K* S! i
7 : BLS S* K* S+ S* B! !
8 : TEST K* L* S= K* “ 0* S* OR 0= i
9 ; 1ST DUP 1 < ODER 26 > OR 0- t
10 ! COMP N* LEN 1 + 2 DO ITH 1ST IF KTH TEST IF BLS THEN
11 ELSE DROP THEN K* L* 8! LOOP t
12 : SOUND NAME FIRST N* LEN 2 > IF COMP THEN S* " 0000"
13 8+ S* S! CR C SOUNDEX CODE* I TYPE S* TYPE CR i
14
Some Examples of the String Handling Package
DECIMAL < I/O in Base 10 )
50 STRING ALPHA < create a string variable ALPHA with a
maximum length of 50 characters )
25 STRING BETA ( create a string variable BETA )
* NOW IS THE TIME" BETA S! < store the literal string
NOW IS THE TIME into BETA )
BETA TYPE ( output the contents of BETA )
NOW IS THE TIME
BETA LEN . < current length of BETA is 15 >
15
BETA MLF.N . < maximum length is 25 )
95
5 10 BETA MID* ( substring consisting of characters 5 thru ;
of BETA )
TYPE < output substring )
IS THE
" AT" 5 6 BETA MID* SUB! ( replace the substring IS with AT
BETA TYPE ( output new BETA contents )
NOW AT THE TIME
6 BETA LEFT* < substring of characters 1 to 6 of BETA )
ALPHA S! < store in ALPHA )
ALPHA TYPE ( output ALPHA )
NOW AT
5 ALPHA RIGHT* ( substring of characters 5 to 6 of ALPHA )
TYPE ( output, )
AT
BETA ALPHA St < concatenate BETA and ALPHA )
ALPHA S' ( store in ALPHA )
ALPHA TYPE ( output, new ALPHA )
NOW AT THE TIMENOW AT
ALPHA LEN . ( current length is 21 )
21
" 12345" BETA S! ( new data for BETA )
BETA UAL . ( convert string to number )
12345
32760 STR* ( convert number into string )
TYPE
32760
(continued on page 45) ■
Number 50
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 43
437
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r-i r— r—i —-i r—i r—t 1
Number 50 Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia Page 45
438
—FI BSEB DIME—
JIVIIR IM iM Il
w.
by Kenneth Drexler
If you want to get away from the slow speed, paper costs
and noise of a teletype or other hard copy terminal, try a
video display. Here is a 6800 video display program for use
wih a memory mapped video board such as SSM’s VB1 or
others using a IK display memory.
The program has a full range of commands including:
Cursor Up, Cursor Down, Cursor Right, Cursor Left, Cursor
On and Off, Home, Erase to End of Line, Backspace, Screen
Clear and, of course, Carriage Return and Line Feed. This
displayed line and page length may be varied up to a maximum
size of 64 characters by 16 lines. All data before being dis¬
played by the program are checked against high and low
masks to see if the data falls within the limits set by these
masks. By changing these masks which are located in RAM,
it is possible to limit the characters to a subset of the full
ASCII alphabet, such as capital or lower case letters only.
The program occupies 435 bytes of memory, is fully re¬
locatable, and may be placed in ROM. It uses 16 bytes of
RAM as temporary storage. The RAM may be located any¬
where in memory. The only address constraint is that the
IK video display RAM must be located starting on a IK
boundary ($0000, $0400, $0800, etc.) The program uses 12
of the 32 ASCII control codes ($0400, $0800, etc.) The
program uses 12 of the 32 ASCII control codes ($00-$IF)
for control.
Use of the program is simple. The character to be displayed
(or control code) is placed in the A Register and a subroutine
branch or jump to the program executed. The program then
stores the character in the A Register at the cursor location
in the video display RAM (or executes the appropriate control
function), computes the address of the next character to be
displayed, and, if the cursor is enabled, stores the cursor char¬
acter at the new location. After setting VNRDY, if neces-
say, control is returned to the calling program. All registers
are preserved.
Sixteen random access memory locations are used to store
variables used by the Program. These variables are listed in
Figure No. 1. The first eight of these, LLNTH, PGLNTH,
MASKLI, MASKHI, PAGE, VNRDY, CURSOR and CURBIT
may be changed to alter the display characteristics. Thus the
data stored at cursor ($FOA6) is used by the program as the
cursor and by changing this data the cursor character may be
changed. LLNTH ($FOA6) and PGLNTH ($FOAl) contain
hex characters used by the program as the maximum line and
page length, respectively. These bytes also control when a car-
Kenneth Drexler-Three Embarcadero Center, Suite 2300,
San Francisco, CA 94111
riage return and line feed is generated by the program and
when the display page is full.
FIGURE 1: RAM VARIABLES
NAME
ADDRESS (Hex)
FUNCTION
LGNTH
FOAO
Line Length
PGLNTH
FOAI
Page Length
MASKLO
FOA2
Low Mask for Data
MASKHI
FOA3
High Mask for Data
PAGE
FOA4
Page Control, 0 = Off, 1 = On
CURBIT
FOAS
Cursor Control, O-Off, 1-On
CURSOR
FOA6
ASCII Code for Cursor
Character
VNRDY
FOA7
Full Page Flag, 1 = Full Page
CURSAV
FOA8
Storage for Data under Cursor
VSAVX
FOA9
Storage for the X Register
CHAR
FOAB
Character psoition (0-63)
LINE
FOAC
Line number (0-15)
CHRPSN
FOAD
Memory address for the next
character to be displayed
Each of the first eight RAM locations must be initialized
before the first subroutine call of the progam. A routine to
perform this function is included in the listing. It sets the
RAM locations to the initial values shown in Figure 2. The
remaining variables are used by the program and should not be
changed.
FIGURE 2: INITIAL RAM VALUES
BYTE
VALUE
(Decimal)
LLNTH
32
PGLNTH
15
MASHLO
32 (ASCII Space)
MASKHI
127 (AS11 Rubout)
PAGE
0 (Off)
CURBIT
25 5 (On)
CURSOR
62 (ASCII >)
The PAGE feature requires some explanation. The PAGE
feature is enabled if PAGE ($FOA4) is set to some value
other than zero. When PAGE is enabled, after the location
for display of the next character is computed, the program
determines if this location is at the end of the page determined
by LLNTH and PGLNTH. If it is, VNRDY set to “1” and no
further characters are accepted for display. The program con-
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 46
Number 50
439
tinues, however, to accept control characters, which allow the
display RAM to be cleared or the cursor to be moved. □
usins
♦THIS PROGRAM IS RELOC¬
ATABLE. THE VIDEO RAM
♦MUST BE LOCATED ON A
♦IK BOUNDARY.
♦RAM ADDRESSES*
000H 27 57
6EQ
VLF
008C 81 OD
CMPA
#CR
080E 27 5A
BEQ
VCR
0918 81 15
CMPA
#ETOND
0812 27 5D
BEQ
ERASLN
0014 81 16
CMPA
#CLEAR
0816 27 5D
BEQ
CLSCRN
0818 81 0B
CMPA
tCUP.UP
001A 27 5B
BEQ
CURUPP
001C 81 84
CMPA
#CURDN
001E 27 43
BEQ
VLF
0028 81 06
CMPA
#CURFW
0022 27 5A
BEQ
CURFWD
0024 81 8E
CMPA
#CURBK
F0A8
ORG
$F0A0
0026 27 5D
BEQ CURBAK
F0A8
LLNTH
RMB
1
8028 81 10
CMPA #HQMUP
F0A1
PGLNTH
RMB
1
002A 27 68
BEQ HOME
F0A2
MASKLO
RMB
1
002C 81 08
CMPA #BS
F0A3
MASKHI
RMB
1
082E 27 66
BEQ DELPRV
F0A4
PAGE
RMB
1
0038 81 18
CMPA tCAN
F0A5
CURB IT
RMB
1
0032 27 6F
BEQ CANCEL
F0A6
CURSOR.
RMB
1
0034 81 17
CMPA #CRONOF
F8A7
VNRDY
RMB
1
0036 27 74
BEQ CURTOG
F0A8
CURSAV
RMB
1
♦CHECK
FOR FULL PAGE
F0R9
VSAVX
RMB
2
0038 7D F0 A7
TST VNRDY
F0AB
CHAR
RMB
1
003B 26 20
BNE VEXIT
F0AC
LINE
RMB
1
♦CHECK
DATA V MASKS
F0AD
CHRPSN
RMB
2
003D 81 F8 A2
CMPA MASKLO
0048 2D IB
BLT VEXIT
DC08
VRAM
EQU
$DC00
0842 B1 F0 A3
CMPA MASKHI
00C-C
VRAMHI
EQU
$DC
8045 22 16
BHI VEXIT
♦STORE
DATA, COMPUTE
♦VIDEO
COMMANDS*
♦NEW POSITION
8047 A7 88
STAA 8,X
000D
CR
EQU
$D
0049 7C F0 AB
INC CHAR
000H
LF
EQU
$A
004C 8D 65
VUP
BSR GPSN1
000B
CURUP
EQU
$B CTRL K
♦SAVE DATA AT NEW POS-
0006
CURFW
EQU
$6 CTRL F
♦ITION,
INSERT CURSOR
000E
CURBK
EQU
$E CTRL N
004E A6 08
LDAA 0,X
0004
CURDN
EQU
$4 CTRL D
0858 87 F8 A8
STAA CURSAV
0017
CRONOF
EQU
$17 CTRL W
0053 7D F8 A5
TST CURBIT
0016
CLEAR
EQU
$16 CTRL V
0856 27 85
BEQ VEXIT
0015
ETOND
EQU
$15 CTRL U
8058 86 F8 A6
LDAA CURSOR
0008
BS
EQU
$8 CTRL H
085B A7 08
STAA 0,X
0010
HOMUP
EQU
$18 CTRL P
♦RESTORE REGS AND EXIT
0018
CAN
EQU
$18 CTRL R
085D 32
VEX IT
PULA
005E 33
PULB
0008
ORG
$0080
005P FE F0 A9
LDX VSAVX
0062 39
RTS
♦ENTRY
AND I
MAIN LOOP*
♦VIDEO
SUBROUTINES*
♦SAVE 1
REGIS
TERS
0000 37
VIDEO
PSHB
0063 8D 58
VLF
BSR RPLCUR
0001 36
PSHA
0065 7C F0 AC
INC LINE
0002 FF F0 A9
STX
VSAVX
8068 28 E2
BRA VUP
0005 FE F8 AD
LDX
CHRPSN
006A 8D 49
VCR
BSR RPLCUR
♦CHECK
FOR i
COMMANDS
006C 7F F8 AB
CLR CHAR
0088 81 8A
CMPA
#LF
006F 20 DB
BRA VUP
(continued)
Page 47
Number 50
440
Dr. Dobb’s Journal of Computer Calisthenics & Orthodontia
0071 8D 48
ERflSLN BSR
ETENO
4
0873 20 D7
BRA
VUP
00EB 26 F6
BNE
SCLOP
0675 20 52
CLSCRN BRA
ESCRN
08EO B6 F0 A1
LOAA
PGLNTH
0077 8D 30
CURUPP
BSR
RPLCUR
00F8 B7 F0 AC
STAA
LINE
0879 7A F0 AC
OEC
LINE
08F3 7F F0 AE
CLR
CHAR.
007C 28 CE
BRA
VUP
00F6 80 4B
BSR
VPSN
007E 80 35
CURFWD
BSR
RPLCUR
08F8 80 Cl
BSR
ETENO
0888 7C F0 AE
INC
CHAR
08FA 33
PULB
0883 28 C7
BRA
VUP
00F8 32
PULA
0085 80 2E
CURBAK
BSR
RPLCUR
08FC 39
RTS
0887 7A F0 AE
DEC
CHAR
00FO 28 CA
ESCRN2
BRA
ESCRN
088A 28 C0
BRA
VUP
♦GET NEW POSITION,
008C 80 27
HOME
BSR
RPLCUR
♦AC-JUST CHAR AND LINE
088E 7F F8 AE
CLR
CHAR
00FF 37
GPSN
PSHB
0891 7F F0 AC
CLR
LINE
0109 36
PSHA
0894 28 B6
BRA
VUP
0101 F6 F0 AE
LOAB
CHAR.
0896 80 10
0ELPRV
BSR
RPLCUR.
0184 2A 0B
BPL
NEXT1
0898 7A F0 AE
DEC
CHAR
0106 F6 F0 A0
LOAB
LLNTH
009B 80 16
BSR
GPSN1
0189 F7 F0 AB
STAB
CHAR
0090 86 20
LOAA
#$20
018C 7A F0 AC
OEC
LINE
089F A7 06
STAA
0, X
018F 28 88
BRA
VCOK
00A1 28 AE
BRA
VUP+2
0111 FI F0 A8
NEXT 1
CMPB
LLNTH
00A3 7F F0 AE
CAN13EL
CLR
CHAR
0114 23 86
BCS
VCOK
00A6 80 06
BSR
GPSN1
0116 7F F0 AE
CLR
CHAR
00A8 80 11
BSR
ETENO
0119 7C F8 AC
INC
LINE
08AH 28 A0
VUP1
BRA
VUP
011C F6 F0 AC
VCOK
LOAB
LINE
08AC 80 07
CURTOG BSR
RPLCUR
011F 2A 04
BPL
NEXT2
08AE 73 F0 A5
COM
CURBIT
0121 7F F0 AC
CLR
LINE
0061 28 9E
BRA
VUP+2
0124 5F
CLRB
00E3 28 4A
GPSN1
BRA
GPSN
0125 F0 F0 A1
NEXT2
SUBB
PGLNTH
0885 B6 F0 A8
RPLCUR LC-AA
CURSAV
0128 2F 0F
BLE
VLOK
0868 A7 80
STAA
0 .. X
012A 70 F0 A4
TST
PAGE
006A 39
RTS
0120 27 05
BEQ
VSCRL
00BB 86 40
ETENO
LOAA
#$40
012F 7C F0 A7
INC
VNRDY
08BO B8 F8 AB
SUBA
CHAR
0132 28 08
BRA
PSNXT
08C0 C6 20
LDAB
#$20
0134 80 A8
VSCRL
BSR
SCROLL
0802 E7 08
ETL0P
STAB
Or X
0136 5A
OECB
00134 08
I NX
0137 26 FB
BNE
VSCRL
08133 4A
OECA
8139 7F F0 A7
VLOK
CLR.
VNRC-V
00136 26 FA
BNE
ETLOF
813C 80 05
PSNXT
BSR
VPSN
00138 39
RTS
013E 32
PULA
0009 CE 00 08
ESCP.N
LDX
#VRAM
013F 33
PULB
00CC 86 20
LOAA
#'■
0140 39
RTS
08CE A7 08
ESLOP
STAA Or X
0141 20 BA
ESCRN1
BRA
ESCRN2
000-0 88
I NX
♦COMPUTE CHRPSN=
000-1 80 E0 08
CPX
#VRAM+1024
♦64+LINE+CHAR+VRAM
0004 26 F8
BNE
ESLOP
8143 7F F8 AO
VPSN
CLR
CHRPSN
0806 7F F0 AB
CLR
CHAR
0146 7F FO AE
CLR
CHRPSN+1
000-9 7F F0 AC
CLR
LINE
0149 B6 FO AC
LOAA
LINE
080-0 20 00
BRA
VUP1
014C C6 86
LOAB
#6
08OE CE DC 08
SCROLL
LOX
#VRAM
014E 48
VGLOP
ASLA
00E1 36
PSHA
014F 79 F9 AC-
ROL
CHRPSN
08E2 37
PSHB
0152 5R
OECB
00E3 A6 40
SCLOP
LOAA
$40 r X
0153 26 F9
BNE
VGLOP
00E5 A? 08
STAA 0,X
0153 B8 F9 AE
ADDA
CHAR
08E7 08
I NX
0158 24 03
BCC
VPSN1
08E8 80 OF 08
CPX
#VRAM+1024-6
015A 7C F0 AO
INC
CHRPSN
Page 48
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Number 50
441
0150 B7 F8 RE
'v'PSNl STflfi CHRPSN+1
0168 86 DC
LDRR #VRRMHI
0162 ee F 8 flO
RDDR CHRFSN
0165 87 F0 RD
STflfi CHRPSN
0168 FE F8 RO
LDX CHRPSN
0168 39
RTS
016C 01
HOP
0160 81
NOP
016E 81
NOP
016F 01
NOP
♦INITIALIZE VIDEO RfiM*
♦CLEAR F8R8-F0RF
0178 CE F8 R0
VDINZ LDX #LLNTH
0173 86 18
LDRR #$18
0175 6F 08
VNZLOF CLP. 0/X
0177 08
I NX
0178 4fi
DECR
0179 26 FR
BNE VNZLOP
♦SET: LLNTH=$28, PGLNTH
*=$0F, MRSKL0=$28
♦HRSDHI=$7F, CURSOR=>r
*CURSOP=ON
0178 CE F0 R8
LDX ILLNTH
017E 86 28
LDRR #$28
0188 R7 08
STAR 8,X
0182 R7 82
STAR 2 , X
0184 86 0F
LDRR #$P
0186 R7 81
STAR 1,X
0188 86 7F
LDRR #$7F
818R R7 83
STAR 2 ,X
018C 86 FF
LDRR #$FF
818E R7 85
STAR 5.. X
8190 86 3E
LDRR #->
0192 R7 86
STAR $6, X
0194 28 RE
BRR ESCRN1
END
NO ERROR<
:S) DETECTED
SlfTlEDI TFIELE
BS
0888
CRN
0018
CANCEL
08R3
CHRP
FORE
CHRPSN
FORD
CLERR
0016
CLSCRN
0875
CR
000D
CRONOF
0817
CUR6RK
0885
CURBIT
F8R5
CURED
000E
CURDN
0084
CURFN
0086
CURFWO
087E
CIJRSRV
F0R8
CURSOR.
F8R6
CURTOG
08AC
CURUP
088E
CURUPP
0077
DELPRV
0096
ER.RSLN
8071
ESCRN
88C9
ESCRN1
0141
ESCRM2
80FD
ESLOP
80CE
ETEND
008E
ETLOP
00C2
ETOHO
0015
GPSN
00FF
GPSN1
88B3
HONE
008C
HOHUP
0818
LF
000H
LINE
F8RC
LLNTH
F0R8
MASKHI
F8R3
MASKLO
F0R2
NEXT1
0111
NEXT2
0125
PRGE
F0R4
PGLNTH
F0R1
PSNXT
013C
RPLCUR
0885
SCLOP
08E3
SCROLL
00DE
VCOK
011C
VCR
006R
VDINZ
0170
VEX IT
085D
VGLOP
014E
VIDEO
0000
VLF
0863
VLOK
0139
VNRDV
F0R7
VNZLOF
8175
VPSN
8143
VPSNl
015D
VRRH
DC88
VRAMHI
00DC
VSRVX
F0RS
VSCRL
8134
VUP
084C
VUP1
80RR
Elfl
Number 50
442
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 49
etters
... AND MORE ON TOP-DOWN
Dear DDJ:
In DDJ # 48, John Culleton, Jr. defended his statement
that PASCAL does not support top-down programming in the
physical construction of the program. I would like to say as an
educator and programmer that I agree fully with his position
that a language that does not have regard for the physical lay¬
out of the program can hardly be called a top-down structured
language. In the final analysis, the physical layout of the pro¬
gram is what people will read and study, like a book, when try¬
ing to understand the program. Without logical placement of
the program code, just reading the source listing can be next to
impossible, especially on a long program. In this respect, a
good BASIC compiler might be more useful than PASCAL, if
the language is used properly in a modular way.
I am seriously reconsidering my jump on the PASCAL
bandwagon, for a return to a language that can produce read¬
able, understandable listings, that can be read in magazine arti¬
cles without a computer science degree. The introduction of
CP/M and the BASIC compiler from Microsoft for the Apple,
with it’s chain and global commands just might offer a more
useful programming environment than PASCAL when it comes
to creating understandable and readable programs.
My experience so far indicates that people are not going to
take to PASCAL without a lot of previous programming ex¬
perience, as the Apple version has already proven that using
PASCAL requires a lot of big system savvy on the part of the
user, and simple implementation of previous BASIC functions
like PEEK and POKE require tremendous machine sophistica¬
tion on the part of the user in creating library units or linking
small assembly subroutines. Contrary to popular belief, PAS¬
CAL is definitely not for the beginning programmer. And
without clear, logically organized program layouts, I am not
sure it’s right for the professional production programmer
either, as one thing is constant in industry, and that is that
programmers come and go like street cars, and it’s a sure bet
the programmer who starts that big PASCAL project, won’t be
the one who finishes it.
Regards, P.O. Box 701
David E. Smith Placentia, CA 92670
However, if I choose to do my coding at the terminal, I
can enter the main line routine first, then insert the subordi¬
nate routines before it, and so on. Any text editor will let you
do that.
It is true that the physical sequence required by PASCAL
makes it a little awkward to read a program, but I believe that
it only takes a little getting used to. I agree that this is a dis¬
advantage of PASCAL, but the ability to compile in one pass
simplifies the compiler and undoubtedly allows it to run in
less memory space. On a small computer, this is a tradeoff well
worth making.
Very truly yours, 1724 Blakemore Rd.
Jim Scott Richmond, VA 23225
Dear DDJ:
It would be a pity if potential users of PASCAL were put
off by John Culleton’s remarks in his letter {DDJ #48), which
seem to be based on a misunderstanding. Top-down program¬
ming in PASCAL is simple and straightforward.
First, standard PASCAL has a FORWARD directive, which
allows a procedure to be called before its body is presented to
the compiler. (See the Draft Standard, Secs 6.6.1,6.6.2 in the
May 1980 issue of Pascal News.) This facility is necessary,
since without it one could not compile co-routines, which call
each other.
Second, and more practically, any reasonably large program
to be compiled on a micro or mini is going to have to make use
of the EXTERNAL directive, which calls separately compiled
procedures stored in a library. This is not standard PASCAL,
but every PASCAL system I have seen provides for it. You
want your utility programs in a library anyway, so that you
can call them whenever you like without having to retype
them at program entry via keyboard, disc, or whatever.
In my opinion, PASCAL is the ideal language for the user
of small computers. (Large ones, too, for that matter, but DDJ
is the small user’s guide and vademecum, and we are looking
out for them in the letter column.) It demands discipline; if
properly used it makes for readable and maintainable pro¬
grams; and you can do anything with it that you ought to
want to do anyway. As compared to the pitchfork, spade and
overalls approach of the average FORTRAN/BASIC user it will
cut debugging time at least in half. Let’s don’t badmouth it by
mistake.
Sincerely, AVB Associates, Inc.
Arthur A. Brown Box 326
Garrett Park, MD 20766
MISCELLANEA
Dear DDJ:
In DDJ #48 John R. Culleton, Jr. gave a detailed argument
as to why he believes top-down programming is impossible in
PASCAL. His entire argument hinges on one sentence in the
middle of the sixth paragraph:
“Note that the physical sequence of the modules is also the
order in which they are written.”
J can find no reason for this statement. A programmer is free
to code his modules in any order he pleases, and then put
them into any physical sequence he pleases.
I use PASCAL on my home computer, and I use top-down
programming. Usually I code the whole program on paper
first. I start, of course, with the main line module, then the
modules subordinate to it, and so on, ending with any little
utility modules that may be required. Then I key them in, usu¬
ally in the physical order required by PASCAL.
Dear DDJ:
Your readers might like to know that the American Sub¬
standards Committee X. 1.5 has recently partially approved a
new phonetic alphabet for voice communications. Here it is:
LETTER CODEWORD
A AISLE
B BDELIUM
C CZAR
D DJAKARTA
E EUPHORIA
G GNOME
H HOUR
I IAN
J JOSE
K KNIGHT
L LLAMA
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 50
Number 50
443
M
MNEMONIC
O
OEDIPAL
P
PHONETIC
Q
QUEUE
R
RWANDA
T
TSAR
U
URN
V
VELDT
w
WRONG
X
XANADU
Y
YVONNE
Z
ZWIEBACK
A typical example of the alphabet in use is this recent ex¬
change :
RECORDING: You really can help keep your phone costs
down, just by looking up numbers in your
phone book, whenever possible. Thanks for
helping.
MA BELL: City and number, please?
CALLER: Taco Bell in San Francisco.
MA BELL: Was that “Paco Bell?”
CALLER: No, “TACO.” “T” as in tsar, “A” as in aisle, “C”
as in czar, “O” as in Oedipal.
MA BELL: Was that “C” as in czar or “T” as in tsar?
CALLER: Yes.
MA BELL: Oh.
Mike Gabrielson M. Gabrielson
Bob Phillips P.O. Box 2692
Ron Adler Stanford, CA 94305
Tom Martin
Jim Munro
Glenda Core
NON-HANDSHAKING SOLUTIONS
Dear DDJ :
In the August issue of Dr. Dobb’s Journal, you published
my letter concerning the non-handshaking situation between
my Heath H-14 printer and my North Star Horizon serial
interface. Thanks to your audience, I was deluged with letters
as well as phone calls. Software solutions outnumbered hard¬
ware solutions about two-to-one.
One hardware solution I received was to interchange pins
4 and 7 at the Heath connector to reverse the RTS and NOT-
RTS signals. The gentleman claimed his H-14 was connected
to serial port 2 of a North Star Horizon and stated that his left
configuration header, package 3D, was wired the same as both
my configuration headers are. Since the right configuration
header, package 4D, controls the second serial port, his solu¬
tion may have worked for him, but not for me!
The simplest hardware solution was provided by A1 Weiner
of Waltham, Massachusetts. Without rewiring the Horizon
header at 4D, all I had to do was change the Heath end of the
cable to move DB-25 connector pin 20 to Heath connector
pin 4 to tap the NOT-RTS signal provided in the Heathkit
modification on DB25 connector pin 15. A1 even provided a
three-line BASIC program to prove that the hand-shaking was
working at 4800 baud!
At first, the solution didn’t work. I finally hooked up my
TVOM and discovered I didn’t have the NOT-RTS signal at
the printer (although I had followed the modification instruc¬
tions during assembly). I had never opened the printer since
its first visit to Heathkit Electronics Center in Seattle and as¬
sumed that they had checked it out thoroughly.
They certainly did! Even though I advised them of the
modification number, they ripped out the additional wiring
underneath the PC board! I’ve rewired the mod, and my H-14
is running along at 4800 baud with full handshaking under
CP/M as well as N*DOS. The fix would have been imple¬
mented two weeks ago instead of this morning had HEC told
me of their action months ago.
Thanks to everybody who replied to my previous letter to
the editor—it’s nice to know I’m not alone in the wilderness
without help! And thank you, Dr. Dobb’s Journal, for publish¬
ing my complaint which triggered all the response.
Cordially, 4807 15th Ave. S.E.
John R. Dye, CPD Lacey, WA 98503
Editor’s note: Herewith an example of the response to J. Dye:
Dear DDJ.
This letter is being printed on an H-14 connected to serial
port 2 of a North Star Horizon using stock I/O drivers for
North Star/UCSD PASCAL; communication rate is set at 4800
baud. I think that we can conclude that the incompatibility
discussed in the referenced letter can be readily resolved.
First of all, the North Star software does not respond to
the software interrupt handshaking provided by the DEC-
style XON/XOFF signalling. It does not need to since the
handshaking can be accomplished using RTS and CTS control
lines which are incorporated in RS-232C. These lines are
properly handled by the North Star software
There are several generations of H-14 printers each having
a different handshaking arrangement. To determine which one
you have, read the description of the interface on H-14
OPERATION manual page 9, being sure to incorporate any
change notices into the manual first. Some of the earlier print¬
ers have a printer busy signal on pin 20 of the DB-25 connec¬
tor which goes positive when the printer can accept data. The
current printer has a similar signal on pin 15 of the DB-25
connector. In these later printers there is also an inverted busy
signal on pin 4 of the DB-25 connector. Unfortunately, none
of these connections is compatible with the configuration
header wiring scheme on page 72 of North Star’s HRZ-D-DOC,
What is needed is to present a signal on pin 4 of the DB-25
connector that will go positive whenever the printer can accept
characters.
Page 8 of the H-14 OPERATION manual shows that by
exchanging pins at the end of the RS-232C cable opposite the
DB-25 connector, we can provide the correct signal on pin 4.
To do this on the later H-14, all one needs to do is use a sharp
tool to extract pins 4 and 7 of the connector, exchange them
and reinsert them. On the earlier H-14, pins 14 and 7 need to
be exchanged.
To complete the interface, the left configuration header,
package 3D, on the North Star motherboard must be strapped
as follows (reference page 72 of HRZ-D-DOC):
pin 1 to pin 12
pin 2 to pin 16
pin 3 to pin 15
pin 4 to pin 14
pin 5 to pin 11
pin 7 to pin 8
pin 9 to pin 10
Number 50
444
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
This interface will allow the USART, package 3A, and the
Software which controls it to interface the H-14 at any baud
rate up to and including 4800.
Sincerely, 2281 Cobble Stone Court
Robert Rennard Dayton, OH 45431
CP/M COMPATIBLE SOFTWARE MARKETING
Dear DDJ:
As the developers of CP/M and MP/M, Digital Research is
preparing a list of vendors of CP/M-compatible software. We
would appreciate the help of readers of your magazine in com¬
piling this list for distribution to all interested persons who
contact us.
If any readers are currently marketing CP/M-compatible
software, please send us any or all literature pertaining to your
software which controls it to interface the H-14 at any baud
rate up to and including 4800.
Thank you, Digital Research
Marilyn Darling P.O. Box 579
Pacific Grove, CA 93950
AT ODDS WITH DDJ
Dear DDJ:
1 have received my copies of Volume 5, Issue 8 of DDJ,
which contains my article ( A Note On 6502 Indirect Addres¬
sing), and I am slightly upset.
I have about 70 papers to my credit, in all kinds of journals,
and this is the very first time that I have not had the courtesy
of having galley proofs to review before an article of mine is
printed.
I understand about your policy of quick publication; I want
to see my ideas on programming published as quickly as pos¬
sible, too —but not with typists’ mistakes still in them! Typists
are not infallible, nor should they be expected to be. For the
record, the mistakes were as follows:
P. 26 col. 1 line 37: “is keep” should be “is to keep”
P. 26 col. 3 line 34: left paren should line up under I
P. 27 col. 1 line 57: “each by” should be “each time by”
P. 27 col. 3 line 11: [1] refers to reference number 1,
which is not marked as such. (I don’t mind if you want to
set up your own conventional notation for references to
journal papers and books, but it has to be consistent with
itself.)
None of these turned out to be really serious, in this case—
which is why I am slightly, rather than considerably, upset.
Sincerely, George Washington University
Professor W. D. Maurer S.E.A.S.
Washington, DC 20052
Prof. Maurer’s objection is well taken and the subject of this
month’s editorial (see p. 1). -JP
SIGNED COMPARISON: ALTERNATE ROUTINE
Dear DDJ:
While scanning the listing of the runtime library for the
Small C compiler in issue #48,1 happened to notice the signed
compare routine (“cccmp”). This routine performs a compari¬
son of two 16-bit signed numbers (two’s complement) by sub¬
tracting one of the numbers from the other and then examin¬
ing the sign of the result. This technique works fine as long as
the difference between the numbers being compared is less
Page 52
than or equal to 32767; however, if the numbers differ by
more than 32767, the result of the compare will be incorrect
due to arithmetic overflow during the calculation.
A different way to accomplish a signed comparison is to
invert the sign bits of the two numbers being compared and
then to perform an unsigned compare using the new numbers.
A routine using this technique is shown below:
; Common routine to perform a signed compare of DE &HL.
; This routine compares DE & HL and sets the conditions:
; Carry reflects sign of difference (set if DE < HL)
; Zero/non-zero set according to equality.
)
cccmp: MOV
A,H
; invert sign of HL.
XRI
80H
MOV
H,A
MOV
A,D
; invert sign of DE.
XRI
8 OH
CMP
H
; compare msbs.
JNZ
cccmpl
; unequal —comparison done.
MOV
A,E
; equal—compare lsbs.
CMP
L
cccmpl: LXI
H,1
; (required by Small C).
RET
This new method works by mapping the signed number do¬
main into the unsigned number domain, where 16-bit com¬
parisons may be easily made, before making the comparison.
A few examples of number mappings are shown below:
Decimal number
Hex number
before map
Hex number
after map
-32768
8000
0000
-32767
8001
0001
-1
FFFF
7FFF
0
0000
8000
1
0001
8001
32767
7FFF
FFFF
Now, does this solve a problem or just create a new prob¬
lem? Consider the two expressions shown below, which appear
to be equivalent:
Expression
New
Old
“Correct’
result
result
result
(-4000 < 30000)
True
False
True
(-4000- 30000 <0)
False
False
False
Because of arithmetic overflow in the second expression,
where “-4000 - 30000” is correctly interpreted as 31536 (not
-34000), the expressions have different values. The new “im¬
proved” compare yields the differing results, depending upon
how the expression is formed; whereas the old compare yields
identical (but incorrect in one case) results no matter which
way the expression is formed. Which attibute appeals to you
more: correctness or apparent consistency? I vote for correct¬
ness in this case.
Yours truly, Neoteric
Harry B. Stewart 15816 San Benito Way
Los Gatos, CA 95030
Number 50
445
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
MORE ON LINKING WITH ERROR CORRECTION
Dear DDJ :
Many thanks for publishing Sylvan Rubin’s note on linking
with error correction (DDJ #48). It is a fine example of a
concise, lucid exposition of an improved technique applicable
to a large class of programs and quite unrelated to any particu¬
lar processor.
I should like to bring to your attention what I consider a
small improvement to Mr. Rubin’s plan. Let the primary link
field contain what Mr. Rubin calls the cross link: (predecessor
address) XOR (successor address). By the method given in the
italicized note this one field affects both forward and back¬
ward linking, if one knows where one has been. Then let the
secondary link field contain the one’s complement of the pri¬
mary link. The one’s complement operation is chosen because
of its sensitivity to stuck (stuck at one, stuck at zero) faults,
which are among the most common machine faults. In the ab-
sense of error the XOR of the two links will be all ones.
Of course this scheme too has its limitations, While each
zero in the XOR of the two links implies that one of them is
wrong, each one may mean that they are both wrong. In that
case, or when successive nodes have link errors one learns the
value of backup copies and checkpointing.
Incidentally, I cannot recommend the practice of “cor¬
recting” any portion of a dataset without notice to the user.
A conscientious user needs to know about errors. That need
is one of the reasons for writing exception reports. Errors rare¬
ly come as single spies; reporting those detected often helps
detect others. If reporting errors makes the report too long
then there are far too many errrors.
Sincerely, Folly Fraction Farm
J. A. MacLaughlin Clarksville, MD 21029
Number 50
446
Dr. Dobb's Journal of Computer Calisthenics & Orthodontia
Page 53
Index
This is an index to articles and programs, but some letters have also been indexed. References are of the
form/ssne numberIpage numbers. Those in normal type are references to programs. References separated by a
comma are connected in some way; those separated by a semicolon are completely distinct. Unless otherwise
marked, a program is in assembly language. Except for author entries the processor type is marked or clear
from the context. In general, a program can be found by author, processor type, and program type.
The following table gives the correspondence between month/year and issue numbers.
Vol 5—1980
January 41
February 42
March 43
April 44
May 45
June/July 46
August 47
September 48
October 49
November/December 50
1802
Cross-assembler [CP/M] 432
Elf 122
6800
Cross-assembler [CP/M] 432
Video-display program 439
8080
And CP/M 396
And Z80 289; 394
Fast fourier transform 164
PILOT 82
Registers in 47 bytes 173
Small C compiler 176
Translator system [to Z80] 216
Unaltered 42
Variations 173
/Z80 indirect addressing 289; 394
8813
Polymorphic math functions 125
9 or 16 bits? [Opcode design] 373
9900 46; 108
Acoustic coupler 351
Addendum
Newberry, S. 395
Addition trick 125
Addressing, indirect
6502 333
8080/Z80 289; 394
Adler, R. 443
ADM-3A 56
Algorithms 130; 169; 207; 264; 350
Allison, D. 73; 169; 207; 264; 350
Alpha listing [H8] 104
ALS-8 to CP/M conversion 24; 261
Animal 350
APPLE
User interface 267
APPLE II
Program renumbering 67
ROM byte-finder 243
Arrays
FORTH 242
North Star 40
Assemblers
6800 + 1802 cross-assembler [CP/M] 432
Table-driven 59; 171
Z80, subroutines 159
Bach, S. 243; 267
Balcom, O. 39
Barker. L. 42; 173; 205; 222; 268; 309
BASIC 42
Memory dump 260
North Star
Cross-reference 147; 151; 339; 382
Patches 40; 171
Statement generator 418
String arrays 40
Two-column display 259
Poly 88 141
Structured 201
Tiny BASIC 201; 356
Bender, A. 209
Bentley, J. 130
Bertollo, D. 348
Binary to decimal conversion 73
Bokelman, J. 42
Borochoff, R. 126
Bronstein, M. 122
Brown, A. 443
Brown, D. 67
Bugs
Small-C 83
Sam 76's CP/M 83
Byte
ROM byte-finder [APPLE II] 248
447
C15;176;191
C, small see Small C
C, tiny see Tiny C
Caesar, A. 309
Cain, R. 176; 312
Calculators 392
Carter, J. 159; 267
Cason, R. 127
Cassette interface 13
Caulkins, D. 230; 284
CDOS 29; 394
Colley, W. 432
Compilers
META II 169
Small C 176; 312
Conley, W. 352
Conversions/converters
ALS-8 to CP/M 24
Binary to Decimal 73
CP/M to UCSD PASCAL 367
Core, G. 443
Corrections
Barker, L. 309
Keay's table 41
Parsons, R. 83
Silverston, S. 172
COSMAC 282
CP/M II
6800 + 1802 cross-assembler 432
AL8-8 to CP/M file converter 24; 261
And CDOS 29; 394
Bug [SAM 76's CP/M] 83
Game 406
Hardcopy device driver programs 341
Linking to Morrow's cassette interface 13
OSI's CP/M 205
PEN 34
Software 4; 32
Table-driven assembler 59
Tiny interpreter [CP/M flavored C] 15
To UCSD PASCAL file conversion 367
Z80, 8080, and CP/M 396
Crockett, T. 79
Cross-assemblers 432
Culleton, J. 125; 352
Da Costa, F. 39
Darling, M. 445
Dea, R. 216
Deane, R. 242; 434
Design
Algorithm 130
Opcode 373
Diablo 268
Digital systems DDOS 127
Displays
6800 439
North Star 259
Documentation 426
Double density system 339
Douds, C. 127
Drexler, K. 439
Dump/Dumping
BASIC 260
Dye, J. 309; 444
Ecklein, D. 394
Elf 268
Elizondo, F. 261
Enhancements
ADM-3A 56
Entry points 267
Equations, differential 392
Errata of computer programming 244
Errors 309; 349; 446
Fiddes, L. 394
File conversion see Conversion
File transfer 375
Flashwriter I 406
Foreign language trainer 423
Formatter, Tl 9900 46; 108
FORTH 242; 434
Frampton, H. 24
Fusfeld, R. 168
Gabrielson, M. 443
Games, CP/M 406
Gammell, J. 40
Garcia, L. 418
Gaugler, G. 345; 423
Gelles, A. 85
Gibson, T. 201
Glitch 222
Go: utility command under CP/M 11
Gordon, H. 324; 373; 395
Gramer, J. 125
Graphics
Flashwriter I [CP/M] 406
Microprocessor-assisted system 79
Guthery, S. 201
Hallen, R. 34
Hamlin, G. 79
Hardcopy device driver programs [CP/M] 341
Head, G. 222
Heath
H-8 104; 287
H-14 201; 332; 395
Hemminger, C. 309
Hex keyboard 122
Holtrichter, J. 339
Horizon [ Interfacing H-14] 395
Howell, J. 173; 266; 396
Hudson, G. 259
Hudson, L. 40; 382
Hudson, R. 356
Hughes, L. 375
Improvements to:
APPLE user interface 267
CP/M and CDOS 394
Zant's modular programming 266
Indirect addressing [8080 & Z80] 289; 333
Installation, Phantom-deselect 42
Interface
APPLE 67
CP/M linked to Morrow's cassette interface 258
H-14 to Horizon 395
WH 14 printer to serial POR 443
Interpreter
LISP 268
Tiny 15
Jamieson, C. 83
Johnson, D. 84
Johnson, R. 171
Johnson, S. 197
448
Keay, C. 41
Kernigham, B. 191
Keyboard, Hex 122
Keyplus integrated utility 309
Kildall, G. 2
Knippenberg, H. 260
Knuth, D. 88; 244
Konopik, M. 234; 332
Kruse, R. 272; 395
Languages
C 191
Foreign 423
META II 142
Syntax-oriented compiler writing language 142
Las Vegas super-slot 406
Lesk, M. 191
Lindenschmitt, G. 84
LISP, interpreter 268
Listing, H-8 104
Logic 348
Long, W. 371
Loughman, W. 431
Love program 345
Lucky, R. 171; 309
Lunsford, D. 172
MacLaughlin, J. 446
Martin, T. 443
Math functions [8813] 125
Mathematical typography 88
Maurer, W. 333; 445
MCALL-C 395
McGaw, J. 125
Memory dump [BASIC] 260
Microchess 126
Microsoft 222
Miller, W. 13
MITS DOS disk to disk copy routine 209
Modular programming 266
Monitors
Elf tiny 268
SYM-1 324
Moore, F. 426
Morrow, G. 13
Moss, W. 104
MOVIT431
Multiple file transfer 375
Munro, J. 443
N-LOGS 400
Naess, 0. 364
Networks 226; 230; 257
Newberry, S. 42; 125
NIBASM 371
North Star see BASIC; Horizon
Number language [N-LOGS] 400
Oliver, J. 39
Opcode design 373
OSI 205
Output [COSMAC 1861] 282
PASCAL 75; 127; 367
Patches, North Star DOS 40
PCNET 230; 284
PEN 34
Personal Computer Network see PCNET
PET 127
Pfafman, F. 42
Phelan, C. 309
Phillips, T. 443
Phone dialer 84
PI LOT 82
Poly 88 BASIC 141
Polymorphic 8813 math functions 125
Price, G. H. 282
Printer [H-14] 332
Probes, logic 348
Programs
6800 439
CP/M 406
CP/M + CDOS compatability 29
Love program 345
User interface to APPLE-11 267
Programmable calculator 392
Programming
BASIC 341
C and tiny C 201
C language 191
CP/M 341
Changing SPI to CP/M 32
Errata 244
Pastimes and pleasures 37; 285; 330
Zant's modular programming 266
Protocol 234
Pugh, T. 234
Purdin, T. 151
Quick-key 418
Quinn, C. 39
Raeside, D. 121
Reentrant formatter [TI9900] 108
Register/storage [8080] 173
Rennard, R. 444
Ritchie, D. 191
ROM byte-finder [APPLE II] 243
Routines
Alternate 445
MITS DOS disk to disk copy 209
Rowland, D. 269
Rubin, S. 349
Rules 309
Runtime library [small C] 312
S. D. board 257
SAM 76 83
Saunders, W. 395
Schorre, D. 142
Scientific computers 400
Scott, J. 443
Serial port 425
Silverston, S. 172
Simons, K. 400
Sippy, L. 425
Sjowall, T. 367
Skjellum, A. 11; 289
Small C
8080 176
Compiler 312
Runtime library 312
Small systems and monitors 324
Smith, B. 267
Smith, D. 443
Smith, W. 240
449
Software
CP/M 4; 445
Software market 309
Source-text area, extended 371
SPI formatted programs 32
Sprenkle, J. 279
SR-52 programmable calculator 392
Statement generator [North Star] 418
Stewart, H. 445
STOIC [North Star disk] 55
Stowe, T. 287
String arrays [North Star] 40
Subroutines [Z-80 assembler] 159
SYM-1 324
Symbol table alpha listing [H8] 104
Syntax-oriented compiler writing language 142
Table driven assembler 59; 171
Terminal parameters [PASCAL] 75
Thomson, B. 223
Tl 9900 45; 108
Tiny BASIC see BASIC
Tiny interpreter 15
Tiny monitor [Elf] 268
Tl PMX [Tl 9900] 46; 108
Top-down 352; 443
Translator [8080 to Z80] 216
TRS-80 441
Typography, mathematical 88
UCSD PASCAL see PASCAL
Utility
Command under CP/M 11
Multiple file transfer 375
Van Buer, D. 59; 171; 268
Video display RAM 439
Vocabulary trainer 423
Wakerley, J. 56
Walters, N. 46; 108
Warner, J. 29
Wasserman, P. 172
Wetherell, C. 37; 77; 285; 330
Wexler, S. 309
WH 14 printer 425
Wilcox, R. 82
Willoughby, S. 341
X-Ref tool [North Star] 339
Yakush, S. 392
Z-80
Assembler 159
Circuit [H-8] 287
Indirect addressing 289; 394
Power increase 172
Translator system from 8080 216
Zant, R. 266
Zeiger, M. 32
ZX65 272; 395
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